Fix Savannah bug #21634, No copy of FDL1.2 included in source code

[findutils.git] / doc / find-maint.texi

\input texinfo @c -*-texinfo-*-
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@settitle Maintaining Findutils
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@include versionmaint.texi

@iftex
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@dircategory GNU organization
@direntry
* Maintaining Findutils: (find-maint).        Maintaining GNU findutils
@end direntry

@copying
This manual explains how GNU findutils is maintained, how changes should
be made and tested, and what resources exist to help developers.

This is edition @value{EDITION}, for findutils version @value{VERSION}.

Copyright @copyright{} 2007 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2
or any later version published by the Free Software Foundation;
with no Invariant Sections, with no
Front-Cover Texts, and with no Back-Cover Texts.
A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
@end copying

@titlepage
@title Maintaining Findutils
@subtitle Edition @value{EDITION}, for GNU findutils version @value{VERSION}
@subtitle @value{UPDATED}
@author by James Youngman

@page
@vskip 0pt plus 1filll
@insertcopying{}
@end titlepage

@contents

@ifnottex
@node Top, Introduction, (dir), (dir)
@top Maintaining GNU Findutils

@insertcopying
@end ifnottex

@menu
* Introduction::
* Maintaining GNU Programs::
* Design Issues::
* Coding Conventions::
* Tools::
* Using the GNU Portability Library::
* Documentation::
* Testing::
* Bugs::
* Distributions::
* Internationalisation::
* Security::
* Making Releases::
* GNU Free Documentation License::
@end menu





@node Introduction
@chapter Introduction

This document explains how to contribute to and maintain GNU
Findutils.  It concentrates on developer-specific issues.  For
information about how to use the software please refer to
@xref{Introduction, ,Introduction,find,The Findutils manual}.

This manual aims to be useful without necessarily being verbose.  It's
also a recent document, so there will be a many areas in which
improvements can be made.  If you find that the document misses out
important information or any part of the document is be so terse as to
be unuseful, please ask for help on the @email{bug-findutils@@gnu.org}
mailing list.  We'll try to improve this document too.


@node Maintaining GNU Programs
@chapter Maintaining GNU Programs

GNU Findutils is part of the GNU Project and so there are a number of
documents which set out standards for the maintenance of GNU
software.

@table @file
@item standards.texi
GNU Project Coding Standards.  All changes to findutils should comply
with these standards.  In some areas we go somewhat beyond the
requirements of the standards, but these cases are explained in this
manual.
@item maintain.texi
Information for Maintainers of GNU Software.  This document provides
guidance for GNU maintainers.  Everybody with commit access should
read this document.   Everybody else is welcome to do so too, of
course.
@end table



@node Design Issues
@chapter Design Issues

The findutils package is installed on many many systems, usually as a
fundamental component.  The programs in the package are often used in
order to successfully boot or fix the system.

This fact means that for findutils we bear in mind considerations that
may not apply so much as for other packages.  For example, the fact
that findutils is often a base component motivates us to
@itemize
@item Limit dependencies on libraries
@item Avoid dependencies on other large packages (for example, interpreters)
@item Be conservative when making changes to the 'stable' release branch
@end itemize

All those considerations come before functionality.  Functional
enhancements are still made to findutils, but these are almost
exclusively introduced in the 'development' release branch, to allow
extensive testing and proving.

Sometimes it is useful to have a priority list to provide guidance
when making design trade-offs.   For findutils, that priority list is:

@enumerate
@item Correctness
@item Standards compliance
@item Security
@item Backward compatibility
@item Performance
@item Functionality
@end enumerate

For example, we support the @code{-exec} action because POSIX
compliance requires this, even though there are security problems with
it and we would otherwise prefer people to use @code{-execdir}.  There
are also cases where some performance is sacrificed in the name of
security.  For example, the sanity checks that @code{find} performs
while traversing a directory tree may slow it down.   We adopt
functional changes, and functional changes are allowed to make
@code{find} slower, but only if there is no detectable impact on users
who don't use the feature.

Backward-incompatible changes do get made in order to comply with
standards (for example the behaviour of @code{-perm -...} changed in
order to comply with POSIX).  However, they don't get made in order to
provide better ease of use; for example the semantics of @code{-size
-2G} are almost always unexpected by users, but we retain the current
behaviour because of backward compatibility and for its similarity to
the block-rounding behaviour of @code{-size -30}.  We might introduce
a change which does not have the unfortunate rounding behaviour, but
we would choose another syntax (for example @code{-size '<2G'}) for
this.

In a general sense, we try to do test-driven development of the
findutils code; that is, we try to implement test cases for new
features and bug fixes before modifying the code to make the test
pass.  Some features of the code are tested well, but the test
coverage for other features is less good.  If you are about to modify
the code for a predicate and aren't sure about the test coverage, use
@code{grep} on the test directories and measure the coverage with
@code{gcov} or another test coverage tool.

Lastly, we try not to depend on having a ``working system''.  The
findutils suite is used for diagnosis of problems, and this applies
especially to @code{find}.  We should ensure that @code{find} still
works on relatively broken systems, for example systems with damaged
@file{/etc/passwd} files.  Another interesting example is the case
where a system is a client of one or more unresponsive NFS servers.
On such a system, if you try to stat all mount points, your program
will hang indefinitely, waiting for the remote NFS server to respond.



@c Installed on many systems
@c Often part of base
@c Needs to work on broken systems (e.g. unresponsive NFS servers,
@c mode-0 files)

@node Coding Conventions
@chapter Coding Conventions

Coding style documents which set out to establish a uniform look and
feel to source code have worthy goals, for example greater ease of
maintenance and readability.  However, I do not believe that in
general coding style guide authors can envisage every situation, and
it is always possible that it might on occasion be necessary to break
the letter of the style guide in order to honour its spirit, or to
better achieve the style guide's goals.

I've certainly seen many style guides outside the free software world
which make bald statements such as ``functions shall have exactly one
return statement''.  The desire to ensure consistency and obviousness
of control flow is laudable, but it is all too common for such bald
requirements to be followed unthinkingly.  Certainly I've seen such
coding standards result in unmaintainable code with terrible
infelicities such as functions containing @code{if} statements nested
nine levels deep.  I suppose such coding standards don't survive in
free software projects because they tend to drive away potential
contributors or tend to generate heated discussions on mailing lists.
Equally, a nine-level-deep function in a free software program would
quickly get refactored, assuming it is obvious what the function is
supposed to do...

Be that as it may, the approach I will take for this document is to
explain some idioms and practices in use in the findutils source code,
and leave it up to the reader's engineering judgement to decide which
considerations apply to the code they are working on, and whether or
not there is sufficient reason to ignore the guidance in current
circumstances.


@menu
* Make the Compiler Find the Bugs::
* The File System Is Being Modified::
* Don't Trust the File System Contents::
* Debugging is For Users Too::
* Factor Out Repeated Code::
@end menu

@node    Make the Compiler Find the Bugs
@section Make the Compiler Find the Bugs

Finding bugs is tedious.  If I have a filesystem containing two
million files, and a find command line should print one million of
them, but in fact it misses out 1%, you can tell the program is
printing the wrong result only if you know the right answer for that
filesystem at that time.  If you don't know this, you may just not
find out about that bug.  For this reason it is important to have a
comprehensive test suite.

The test suite is of course not the only way to find the bugs.  The
findutils source code makes liberal use of the assert macro.  While on
the one hand these might be a performance drain, the performance
impact of most of these is negligible compared to the time taken to
fetch even one sector from a disk drive.

Assertions should not be used to check the results of operations which
may be affected by the program's external environment.  For example,
never assert that a file could be opened successfully.  Errors
relating to problems with the program's execution environment should
be diagnosed with a user-oriented error message.  An assertion failure
should always denote a bug in the program.

Several programs in the findutils suite perform self-checks.  See for
example the function @code{pred_sanity_check} in @file{find/pred.c}.
This is generally desirable.

There are also a number of small ways in which we can help the
compiler to find the bugs for us.

@subsection Constants in Equality Testing

It's a common error to write @code{=} when @code{==} is meant.
Sometimes this happens in new code and is simply due to finger
trouble.  Sometimes it is the result of the inadvertent deletion of a
character.  In any case, there is a subset of cases where we can
persuade the compiler to generate an error message when we make this
mistake; this is where the equality test is with a constant.

This is an example of a vulnerable piece of code.

@example
if (x == 2)
 ...
@end example

A simple typo converts the above into

@example
if (x = 2)
 ...
@end example

We've introduced a bug; the condition is always true, and the value of
@code{x} has been changed.  However, a simple change to our practice
would have made us immune to this problem:

@example
if (2 == x)
 ...
@end example

Usually, the Emacs keystroke @kbd{M-t} can be used to swap the operands.


@subsection Spelling of ASCII NUL

Strings in C are just sequences of characters terminated by a NUL.
The ASCII NUL character has the numerical value zero.  It is normally
represented in C code as @samp{\0}.  Here is a typical piece of C
code:

@example
*p = '\0';
@end example

Consider what happens if there is an unfortunate typo:

@example
*p = '0';
@end example

We have changed the meaning of our program and the compiler cannot
diagnose this as an error.  Our string is no longer terminated.  Bad
things will probably happen.  It would be better if the compiler could
help us diagnose this problem.

In C, the type of @code{'\0'} is in fact int, not char.  This provides
us with a simple way to avoid this error.  The constant @code{0} has
the same value and type as the constant @code{'\0'}.  However, it is
not as vulnerable to typos.    For this reason I normally prefer to
use this code:

@example
*p = 0;
@end example


@node    Factor Out Repeated Code
@section Factor Out Repeated Code

Repeated code imposes a greater maintenance burden and increases the
exposure to bugs.  For example, if you discover that something you
want to implement has some similarity with an existing piece of code,
don't cut and paste it.  Instead, factor the code out.  The risk of
cutting and pasting the code, particularly if you do this several
times, is that you end up with several copies of the same code.

If the original code had a bug, you now have N places where this needs
to be fixed.  It's all to easy to miss some out when trying to fix the
bug.  Equally, it's quite possible that when pasting the code into
some function, the pasted code was not quite adapted correctly to its
new environment.  To pick a contrived example, perhaps it modifies a
global variable which it that code shouldn't be touching in its new
home.  Worse, perhaps it makes some unstated assumption about the
nature of the input arguments which is in fact not true for the
context of the now duplicated code.

A good example of the use of refactoring in findutils is the
@code{collect_arg} function in @file{find/parser.c}.  A less clear-cut
but larger example is the factoring out of code which would otherwise
have been duplicated between @file{find/find.c} and
@code{find/ftsfind.c}.

The findutils test suite is comprehensive enough that refactoring code
should not generally be a daunting prospect from a testing point of
view.  Nevertheless there are some areas which are only
lightly-tested:

@enumerate
@item Tests on the ages of files
@item Code which deals with the values returned by operating system calls (for example handling of ENOENT)
@item Code dealing with OS limits (for example, limits on path length
or exec arguments)
@item Code relating to features not all systems have (for example
Solaris Doors)
@end enumerate

Please exercise caution when working in those areas.


@node    Debugging is For Users Too
@section Debugging is For Users Too

Debug and diagnostic code is often used to verify that a program is
working in the way its author thinks it should be.  But users are
often uncertain about what a program is doing, too.  Exposing them a
little more diagnostic information can help.  Much of the diagnostic
code in @code{find}, for example, is controlled by the @samp{-D} flag,
as opposed to C preprocessor directives.

Making diagnostic messages available to users also means that the
phrasing of the diagnostic messages becomes important, too.


@node    Don't Trust the File System Contents
@section Don't Trust the File System Contents

People use @code{find} to search in directories created by other
people.  Sometimes they do this to check to suspicious activity (for
example to look for new setuid binaries).  This means that it would be
bad if @code{find} were vulnerable to, say, a security problem
exploitable by constructing a specially-crafted filename.  The same
consideration would apply to @code{locate} and @code{updatedb}.

Henry Spencer said this well in his fifth commandment:
@quotation
Thou shalt check the array bounds of all strings (indeed, all arrays),
for surely where thou typest @samp{foo} someone someday shall type
@samp{supercalifragilisticexpialidocious}.
@end quotation

Symbolic links can often be a problem.  If @code{find} calls
@code{lstat} on something and discovers that it is a directory, it's
normal for @code{find} to recurse into it.  Even if the @code{chdir}
system call is used immediately, there is still a window of
opportunity between the @code{lstat} and the @code{chdir} in which a
malicious person could rename the directory and substitute a symbolic
link to some other directory.

@node    The File System Is Being Modified
@section The File System Is Being Modified

The filesystem gets modified while you are traversing it.  For,
example, it's normal for files to get deleted while @code{find} is
traversing a directory.  Issuing an error message seems helpful when a
file is deleted from the one directory you are interested in, but if
@code{find} is searching 15000 directories, such a message becomes
less helpful.

Bear in mind also that it is possible for the directory @code{find} is
currently searching could be moved to another point in the filesystem,
and that the directory in which @code{find} was started could be
deleted.

Henry Spencer's sixth commandment is also apposite here:
@quotation
If a function be advertised to return an error code in the event of
difficulties, thou shalt check for that code, yea, even though the
checks triple the size of thy code and produce aches in thy typing
fingers, for if thou thinkest ``it cannot happen to me'', the gods
shall surely punish thee for thy arrogance.
@end quotation

There are a lot of files out there.  They come in all dates and
sizes.  There is a condition out there in the real world to exercise
every bit of the code base.  So we try to test that code base before
someone falls over a bug.


@node Tools
@chapter Tools
Most of the tools required to build findutils are mentioned in the
file @file{README-CVS}.  We also use some other tools:

@table @asis
@item System call traces
Much of the execution time of find is spent waiting for filesystem
operations.  A system call trace (for example, that provided by
@code{strace}) shows what system calls are being made.   Using this
information we can work to remove unnecessary file system operations.

@item Valgrind
Valgrind is a tool which dynamically verifies the memory accesses a
program makes to ensure that they are valid (for example, that the
behaviour of the program does not in any way depend on the contents of
uninitialised memory).

@item DejaGnu
DejaGnu is the test framework used to run the findutils test suite
(the @code{runtest} program is part of DejaGnu).  It would be ideal if
everybody building @code{findutils} also ran the test suite, but many
people don't have DejaGnu installed.  When changes are made to
findutils, DejaGnu is invoked a lot. @xref{Testing}, for more
information.
@end table

@node Using the GNU Portability Library
@chapter Using the GNU Portability Library
The Gnulib library (@url{http://www.gnu.org/software/gnulib/}) makes a
variety of systems look more like a GNU/Linux system and also applies
a bunch of automatic bug fixes and workarounds.  Some of these also
apply to GNU/Linux systems too.  For example, the Gnulib regex
implementation is used when we determine that we are building on a
GNU libc system with a bug in the regex implementation.


@section How and Why we Import the Gnulib Code
Gnulib does not have a release process which results in a source
tarball you can download.  Instead, the code is simply made available
by CVS.

GNU projects vary in how they interact with Gnulib.  Many import a
selection of code from Gnulib into the working directory and then
check the updated files into the CVS repository for their project.
The coreutils project does this, for example.

At the last maintainer changeover for findutils (2003) it turned out
that there was a lot of material in findutils in common with Gnulib,
but it had not been updated in a long time.  It was difficult to
figure out which source files were intended to track external sources
and which were intended to contain incompatible changes, or diverge
for other reasons.

To reduce this uncertainty, I decided to treat Gnulib much like
Automake.  Files supplied by Automake are simply absent from the
findutils source tree.  When Automake is run with @code{automake
--add-missing --copy}, it adds in all the files it thinks should be
there which aren't there already.

An analogous approach is taken with Gnulib.  The Gnulib code is
imported from the CVS repository for Gnulib with a findutils helper
script, @code{import-gnulib.sh}.  That script fetches a copy of the
Gnulib code into the subdirectory @file{gnulib-cvs} and then runs
@code{gnulib-tool}.  The @code{gnulib-tool} program copies the
required parts of Gnulib into the findutils source tree in the
subdirectory @file{gnulib}.  This process gives us the property that
the code in @file{gnulib} and @code{gnulib-cvs} is not included in the
findutils CVS tree.   Both directories are listed in @file{.cvsignore}
and so CVS ignores them.

Findutils does not use all the Gnulib code.  The modules we need are
listed in the file @file{import-gnulib.config}.  The same file also
indicates the version of Gnulib that we want to use.  Since Gnulib has
no actual release process, we just use a date.  Both
@file{import-gnulib.sh} and @file{import-gnulib.config} are in the
findutils CVS repository.

The upshot of all this is that we can use the findutils CVS repository
to track which version of Gnulib every findutils release uses.  That
information is also provided when the user invokes a findutils program
with the @samp{--version} option.  It also means that if a file exists
in the Findutils CVS repository, you can be certain that the file
exists in the CVS repository and is different from a similar file
elsewhere, it's for a reason.

There are a small number of exceptions to this; the standard
boiler-plate GNU files such as @file{ABOUT-NLS}, @file{INSTALL} and
@file{COPYING}.


@section How We Fix Gnulib Bugs
If we always directly import the Gnulib code directly from the CVS
repository in this way, it is impossible to maintain a locally
different copy of Gnulib.  This is often a benefit in that accidental
version skew is prevented.

However, sometimes we want deliberate version skew in order to use a
findutils-specific patched version of a Gnulib file, for example
because we fixed a bug.

Gnulib is used by quite a number of GNU projects, and this means that
it gets plenty of testing.  Therefore there are relatively few bugs in
the Gnulib code, but it does happen from time to time.

However, since there is no waiting around for a Gnulib source release
tarball, Gnulib bugs are generally fixed quickly.  Here is an outline
of the way we would contribute a fix to Gnulib (assuming you know it
is not already fixed in current Gnulib CVS):

@table @asis
@item Check you already completed a copyright assignment for Gnulib
@item Begin with a vanilla CVS tree
Download the Findutils source code from CVS (or use the tree you have
already)
@item Check out a copy of the Gnulib source
An easy way to do this is to simply use @code{cp -ar} on the
@file{gnulib-cvs} directory.   Have the Gnulib code checked out
somewhere @emph{outside} your working CVS tree for findutils.
@item Import Gnulib from your local copy
The @code{import-gnulib.sh} tool has a @samp{-d} option which you can
use to import the code from a local copy of Gnulib.
@item Build findutils
Build findutils and run the test suite, which should pass.  In our
example we assume you have just noticed a bug in Gnulib, not that
recent Gnulib changes broke the findutils regression tests.
@item Write a test case
If in fact Gnulib did break the findutils regression tests, you can probably
skip this step, since you already have a test case demonstrating the problem.
Otherwise, write a findutils test case for the bug and/or a Gnulib test case.
@item Fix the Gnulib bug
Make sure your editor follows symbolic links so that your changes to
@file{gnulib/...} actually affect the files in the CVS working
directory you checked out earlier.   Observe that your test now passes.
@item Prepare a Gnulib patch
Use @code{cvs -z3 diff -upN} to prepare the patch.  Write a ChangeLog
entry and prepend this to the patch.  Check that the patch conforms
with the GNU coding standards, and email it to the Gnulib mailing
list.
@item Wait for the patch to be applied
Once your bug fix has been applied, you can update your local directory
from CVS, re-import the code into Findutils (still using the @code{-d}
option), and re-run the tests.  This verifies that the fix the Gnulib
team made actually fixes your problem.
@item Reimport the Gnulib code
Update the findutils file @file{import-gnulib.config} to specify a
date which is after the point at which the bug fix was committed to
Gnulib.  Finally, re-import the Gnulib code directly from CVS by using
@samp{import-gnulib.sh} without the @samp{-d} option, and run the
tests again.  This verifies that there was no remaining local change
that we were relying on to fix the bug.

Be aware of the fact that the date specified in the
@file{import-gnulib.config} file selects the latest changes for the
given date, so if you modify @file{import-gnulib.config} as soon as
someone tells you they they checked in a bugfix and you set
@var{gnulib_version} to today's date, there will be some file version
instability for the rest of the day.

@end table

@node Documentation
@chapter Documentation

The findutils CVS tree includes several different types of
documentation.

@section User Documentation
User-oriented documentation is provided as manual pages and in
Texinfo.  See
@ref{Introduction,,Introduction,find,The Findutils manual}.

Please make sure both sets of documentation are updated if you make a
change to the code.  The GNU coding standards do not normally call for
maintaining manual pages on the grounds of effort duplication.
However, the manual page format is more convenient for quick
reference, and so it's worth maintaining both types of documentation.
However, the manual pages are normally rather more terse than the
Texinfo documentation.  The manual pages are suitable for reference
use, but the Texinfo manual should also include introductory and
tutorial material.


@section Build Guidance

@table @file
@item ABOUT-NLS
Describes the Free Translation Project, the translation status of
various GNU projects, and how to participate by translating an
application.
@item AUTHORS
Lists the authors of findutils.
@item COPYING
The copyright license covering findutils; currently, the GNU GPL,
version 3.
@item INSTALL
Generic installation instructions for installing GNU programs.
@item README
Information about how to compile findutils in particular
@item README-alpha
A README file which is included with testing releases of findutils.
@item README-CVS
Describes how to build findutils from the code in CVS.
@item THANKS
Thanks for people who contributed to findutils.  Generally, if
someone's contribution was significant enough to need a copyright
assignment, their name should go in here.
@item TODO
Mainly obsolete.
@end table


@section Release Information
@table @file
@item NEWS
Enumerates the user-visible change in each release.  Typical changes
are fixed bugs, functionality changes and documentation changes.
Include the date when a release is made.
@item ChangeLog
This file enumerates all changes to the findutils source code (with
the possible exception of @file{.cvsignore} and @code{.gitignore}
changes).  The level of detail used for this file should be sufficient
to answer the questions ``what changed?'' and ``why was it changed?''.
If a change fixes a bug, always give the bug reference number in both
the @file{ChangeLog} and @file{NEWS} files and of course also in the
checkin message.  In general, it should be possible to enumerate all
material changes to a function by searching for its name in
@file{ChangeLog}.  Mention when each release is made.
@end table

@node Testing
@chapter Testing
This chapter will explain the general procedures for adding tests to
the test suite, and the functions defined in the findutils-specific
DejaGnu configuration.  Where appropriate references will be made to
the DejaGnu documentation.

@node Bugs
@chapter Bugs

Bugs are logged in the Savannah bug tracker
@url{http://savannah.gnu.org/bugs/?group=findutils}.  The tracker
offers several fields but their use is largely obvious.  The
life-cycle of a bug is like this:


@table @asis
@item Open
Someone, usually a maintainer, a distribution maintainer or a user,
creates a bug by filling in the form.   They fill in field values as
they see fit.  This will generate an email to
@email{bug-findutils@@gnu.org}.

@item Triage
The bug hangs around with @samp{Status=None} until someone begins to
work on it.  At that point they set the ``Assigned To'' field and will
sometimes set the status to @samp{In Progress}, especially if the bug
will take a while to fix.

@item Non-bugs
Quite a lot of reports are not actually bugs; for these the usual
procedure is to explain why the problem is not a bug, set the status
to @samp{Invalid} and close the bug.   Make sure you set the
@samp{Assigned to} field to yourself before closing the bug.

@item Fixing
When you commit a bug fix into CVS (or in the case of a contributed
patch, commit the change), mark the bug as @samp{Fixed}.  Make sure
you include a new test case where this is relevant.  If you can figure
out which releases are affected, please also set the @samp{Release}
field to the earliest release which is affected by the bug.
Indicate which source branch the fix is included in (for example,
4.2.x or 4.3.x).  Don't close the bug yet.

@item Release
When a release is made which includes the bug fix, make sure the bug
is listed in the NEWS file.  Once the release is made, fill in the
@samp{Fixed Release} field and close the bug.
@end table


@node Distributions
@chapter Distributions
Almost all GNU/Linux distributions include findutils, but only some of
them have a package maintainer who is a member of the mailing list.
Distributions don't often feed back patches to the
@email{bug-findutils@@gnu.org} list, but on the other hand many of
their patches relate only to standards for file locations and so
forth, and are therefore distribution specific.  On an irregular basis
I check the current patches being used by one or two distributions,
but the total number of GNU/Linux distributions is large enough that
we could not hope to cover them all.

Often, bugs are raised against a distribution's bug tracker instead of
GNU's.    Periodically (about every six months) I take a look at some
of the more accessible bug trackers to indicate which bugs have been
fixed upstream.

Many distributions include both findutils and the slocate package,
which provides a replacement @code{locate}.


@node Internationalisation
@chapter Internationalisation
Translation is essentially automated from the maintainer's point of
view.  The TP mails the maintainer when a new PO file is available,
and we just download it and check it in.  We copy the @file{.po} files
into the CVS repository.  For more information, please see
@url{http://www.iro.umontreal.ca/translation/HTML/domain-findutils.html}.


@node Security
@chapter Security

See @ref{Security Considerations, ,Security Considerations,find,The
Findutils manual}, for a full description of the findutils approach to
security considerations and discussion of particular tools.

If someone reports a security bug publicly, we should fix this as
rapidly as possible.  If necessary, this can mean issuing a fixed
release containing just the one bug fix.  We try to avoid issuing
releases which include both significant security fixes and functional
changes.

Where someone reports a security problem privately, we generally try
to construct and test a patch without checking the intermediate code
in.  Once everything has been tested, this allows us to commit a patch
and immediately make a release.   The advantage of doing things this
way is that we avoid situations where people watching for CVS commits
can figure out and exploit a security problem before a fixed release
is available.

It's important that security problems be fixed promptly, but don't
rush so much that things go wrong.  Make sure the new release really
fixes the problem.  It's usually best not to include functional
changes in your security-fix release.

If the security problem is serious, send an alert to
@email{vendor-sec@@lst.de}.  The members of the list include most
GNU/Linux distributions.  The point of doing this is to allow them to
prepare to release your security fix to their customers, once the fix
becomes available.    Here is an example alert:-

@smallexample
GNU findutils heap buffer overrun (potential privilege escalation)

$Revision: 1.4 $; $Date: 2007/11/26 10:28:00 $


I. BACKGROUND
=============

GNU findutils is a set of programs which search for files on Unix-like
systems.  It is maintained by the GNU Project of the Free Software
Foundation.  For more information, see
@url{http://www.gnu.org/software/findutils}.


II. DESCRIPTION
===============

When GNU locate reads filenames from an old-format locate database,
they are read into a fixed-length buffer allocated on the heap.
Filenames longer than the 1026-byte buffer can cause a buffer overrun.
The overrunning data can be chosen by any person able to control the
names of filenames created on the local system.  This will normally
include all local users, but in many cases also remote users (for
example in the case of FTP servers allowing uploads).

III. ANALYSIS
=============

Findutils supports three different formats of locate database, its
native format "LOCATE02", the slocate variant of LOCATE02, and a
traditional ("old") format that locate uses on other Unix systems.

When locate reads filenames from a LOCATE02 database (the default
format), the buffer into which data is read is automatically extended
to accomodate the length of the filenames.

This automatic buffer extension does not happen for old-format
databases.  Instead a 1026-byte buffer is used.  When a longer
pathname appears in the locate database, the end of this buffer is
overrun.  The buffer is allocated on the heap (not the stack).

If the locate database is in the default LOCATE02 format, the locate
program does perform automatic buffer extension, and the program is
not vulnerable to this problem.  The software used to build the
old-format locate database is not itself vulnerable to the same
attack.

Most installations of GNU findutils do not use the old database
format, and so will not be vulnerable.


IV. DETECTION
=============

Software
--------
All existing releases of findutils are affected.


Installations
-------------

To discover the ongest path name on a given system, you can use the
following command (requires GNU findutils and GNU coreutils):

@verbatim
find / -print0 | tr -c '\0' 'x' | tr '\0' '\n' | wc -L
@end verbatim

V. EXAMPLE
==========

This section includes a shell script which determines which of a list
of locate binaries is vulnerable to the problem.  The shell script has
been tested only on glibc based systems having a mktemp binary.

NOTE: This script deliberately overruns the buffer in order to
determine if a binary is affected.  Therefore running it on your
system may have undesirable effects.  We recommend that you read the
script before running it.

@verbatim
#! /bin/sh
set +m
if vanilla_db="$(mktemp nicedb.XXXXXX)" ; then
    if updatedb --prunepaths="" --old-format --localpaths="/tmp" \
        --output="$@{vanilla_db@}" ; then
        true
    else
        rm -f "$@{vanilla_db@}"
        vanilla_db=""
        echo "Failed to create old-format locate database; skipping the sanity checks" >&2
    fi
fi

make_overrun_db() @{
    # Start with a valid database
    cat "$@{vanilla_db@}"
    # Make the final entry really long
    dd if=/dev/zero  bs=1 count=1500 2>/dev/null | tr '\000' 'x'
@}



ulimit -c 0

usage() @{ echo "usage: $0 binary [binary...]" >&2; exit $1; @}
[ $# -eq 0 ] && usage 1

bad=""
good=""
ugly=""
if dbfile="$(mktemp nasty.XXXXXX)"
then
    make_overrun_db > "$dbfile"
    for locate ; do
      ver="$locate = $("$locate"  --version | head -1)"
      if [ -z "$vanilla_db" ] || "$locate" -d "$vanilla_db" "" >/dev/null ; then
          "$locate" -d "$dbfile" "" >/dev/null
          if [ $? -gt 128 ] ; then
              bad="$bad
vulnerable: $ver"
          else
              good="$good
good: $ver"
          fi
       else
          # the regular locate failed
          ugly="$ugly
buggy, may or may not be vulnerable: $ver"
       fi
    done
    rm -f "$@{dbfile@}" "$@{vanilla_db@}"
    # good: unaffected.  bad: affected (vulnerable).
    # ugly: doesn't even work for a normal old-format database.
    echo "$good"
    echo "$bad"
    echo "$ugly"
else
  exit 1
fi
@end verbatim




VI. VENDOR RESPONSE
===================

The GNU project discovered the problem while 'locate' was being worked
on; this is the first public announcement of the problem.

The GNU findutils mantainer has issued a patch as p[art of this
announcement.  The patch appears below.

A source release of findutils-4.2.31 will be issued on 2007-05-30.
That release will of course include the patch.  The patch will be
committed to the public CVS repository at the same time.  Public
announcements of the release, including a description of the bug, will
be made at the same time as the release.

A release of findutils-4.3.x will follow and will also include the
patch.


VII. PATCH
==========

This patch should apply to findutils-4.2.23 and later.
Findutils-4.2.23 was released almost two years ago.
@verbatim
Index: locate/locate.c
===================================================================
RCS file: /cvsroot/findutils/findutils/locate/locate.c,v
retrieving revision 1.58.2.2
diff -u -p -r1.58.2.2 locate.c
--- locate/locate.c     22 Apr 2007 16:57:42 -0000      1.58.2.2
+++ locate/locate.c     28 May 2007 10:18:16 -0000
@@@@ -124,9 +124,9 @@@@ extern int errno;

 #include "locatedb.h"
 #include <getline.h>
-#include "../gnulib/lib/xalloc.h"
-#include "../gnulib/lib/error.h"
-#include "../gnulib/lib/human.h"
+#include "xalloc.h"
+#include "error.h"
+#include "human.h"
 #include "dirname.h"
 #include "closeout.h"
 #include "nextelem.h"
@@@@ -468,10 +468,36 @@@@ visit_justprint_unquoted(struct process_
   return VISIT_CONTINUE;
 @}

+static void
+toolong (struct process_data *procdata)
+@{
+  error (1, 0,
+        _("locate database %s contains a "
+          "filename longer than locate can handle"),
+        procdata->dbfile);
+@}
+
+static void
+extend (struct process_data *procdata, size_t siz1, size_t siz2)
+@{
+  /* Figure out if the addition operation is safe before performing it. */
+  if (SIZE_MAX - siz1 < siz2)
+    @{
+      toolong (procdata);
+    @}
+  else if (procdata->pathsize < (siz1+siz2))
+    @{
+      procdata->pathsize = siz1+siz2;
+      procdata->original_filename = x2nrealloc (procdata->original_filename,
+                                               &procdata->pathsize,
+                                               1);
+    @}
+@}
+
 static int
 visit_old_format(struct process_data *procdata, void *context)
 @{
-  register char *s;
+  register size_t i;
   (void) context;

   /* Get the offset in the path where this path info starts.  */
@@@@ -479,20 +505,35 @@@@ visit_old_format(struct process_data *pr
     procdata->count += getw (procdata->fp) - LOCATEDB_OLD_OFFSET;
   else
     procdata->count += procdata->c - LOCATEDB_OLD_OFFSET;
+  assert(procdata->count > 0);

-  /* Overlay the old path with the remainder of the new.  */
-  for (s = procdata->original_filename + procdata->count;
+  /* Overlay the old path with the remainder of the new.  Read
+   * more data until we get to the next filename.
+   */
+  for (i=procdata->count;
        (procdata->c = getc (procdata->fp)) > LOCATEDB_OLD_ESCAPE;)
-    if (procdata->c < 0200)
-      *s++ = procdata->c;              /* An ordinary character.  */
-    else
-      @{
-       /* Bigram markers have the high bit set. */
-       procdata->c &= 0177;
-       *s++ = procdata->bigram1[procdata->c];
-       *s++ = procdata->bigram2[procdata->c];
-      @}
-  *s-- = '\0';
+    @{
+      if (procdata->c < 0200)
+       @{
+         /* An ordinary character. */
+         extend (procdata, i, 1u);
+         procdata->original_filename[i++] = procdata->c;
+       @}
+      else
+       @{
+         /* Bigram markers have the high bit set. */
+         extend (procdata, i, 2u);
+         procdata->c &= 0177;
+         procdata->original_filename[i++] = procdata->bigram1[procdata->c];
+         procdata->original_filename[i++] = procdata->bigram2[procdata->c];
+       @}
+    @}
+
+  /* Consider the case where we executed the loop body zero times; we
+   * still need space for the terminating null byte.
+   */
+  extend (procdata, i, 1u);
+  procdata->original_filename[i] = 0;

   procdata->munged_filename = procdata->original_filename;
@end verbatim


VIII. THANKS
============

Thanks to Rob Holland <rob@@inversepath.com> and Tavis Ormandy.


VIII. CVE INFORMATION
=====================

No CVE candidate number has yet been assigned for this vulnerability.
If someone provides one, I will include it in the public announcement
and change logs.
@end smallexample

The original announcement above was sent out with a cleartext PGP
signature, of course, but that has been omitted from the example.

Once a fixed release is available, announce the new release using the
normal channels.  Any CVE number assigned for the problem should be
included in the @file{ChangeLog} and @file{NEWS} entries. See
@url{http://cve.mitre.org/} for an explanation of CVE numbers.



@node Making Releases
@chapter Making Releases
This section will explain how to make a findutils release.   For the
time being here is a terse description of the main steps:

@enumerate
@item Commit changes; make sure your working directory has no
uncommitted changes.
@item Test; make sure that all changes you have made have tests, and
that the tests pass.  Verify this with @code{make distcheck}.
@item Bugs; make sure all Savannah bug entries fixed in this release
are fixed.
@item NEWS; make sure that the NEWS and configure.in file are updated
with the new release number (and checked in).
@item Build the release tarball; do this with @code{make distcheck}.
Copy the tarball somewhere safe.
@item Tag the release; findutils releases are tagged in CVS as
FINDUTILS_x_y_z-1.  For example, the tag for findutils release 4.3.8
is FINDUTILS_4_3_8-1.
@item Prepare the upload and upload it.
@xref{Automated FTP Uploads, ,Automated FTP
Uploads, maintain, Information for Maintainers of GNU Software},
for detailed upload instructions.
@item Make a release announcement; include an extract from the NEWS
file which explains what's changed.  Announcements for test releases
should just go to @email{bug-findutils@@gnu.org}.  Announcements for
stable releases should go to @email{info-gnu@@gnu.org} as well.
@item Bump the release numbers in CVS; edit the @file{configure.in}
and @file{NEWS} files to advance the release numbers.   For example,
if you have just released @samp{4.6.2}, bump the release number to
@samp{4.6.3-CVS}.  The point of the @samp{-CVS} suffix here is that a
findutils binary built from CVS will bear a release number indicating
it's not built from the the ``official'' source release.
@item Close bugs; any bugs recorded on Savannah which were fixed in this
release should now be marked as closed.   Update the @samp{Fixed
Release} field of these bugs appropriately and make sure the
@samp{Assigned to} field is populated.
@end enumerate


@node GNU Free Documentation License
@appendix GNU Free Documentation License
@include fdl.texi

@bye

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@comment LocalWords: var deffn texi deffnx itemx emph asis
@comment LocalWords: findex smallexample subsubsection cindex
@comment LocalWords: dircategory direntry itemize

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@comment LocalWords: sysdep noleaf ls inum xdev filesystems usr atime
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@comment LocalWords: joeuser Kaveh localpaths localuser LOGNAME
@comment LocalWords: Meyering mv netpaths netuser nonblank nonblanks
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@comment LocalWords: prunepaths pwd RFS rmadillo rmdir rsh sbins str
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@comment LocalWords: timestamp timestamps Solaris FreeBSD OpenBSD POSIX