From: Chris Frey <cdfrey@foursquare.net>
Date: Thu, 24 Oct 2013 22:52:44 +0000 (-0400)
Subject: Change th_get_size() macro to return unsigned int
X-Git-Url: https://repo.or.cz/w/libtar.git/commitdiff_plain/e4c1f2974258d6a325622cfd712873d49b5e7a73

Change th_get_size() macro to return unsigned int

On systems where size_t is larger than an int (and larger than
unsigned int), then in various places in the library, where
stuff like this happens:

	size_t sz = th_get_size(t);

then the int value returned from th_get_size() is sign extended to
some unwieldy amount.

On 64bit systems, this can yield extremely large values.

By fixing this problem in the header, and only for th_get_size(),
we avoid breaking the API of the function call oct_to_int()
(which arguably should return an unsigned int, since the sscanf()
it uses expects to yield an unsigned int).  We also fix the library,
which uses th_get_size() internally to assign sizes to size_t.

The drawback is that not all client code that uses th_get_size()
will be fixed, until they recompile, but they will automatically
take advantage of the bugs fixed *inside* the library.

The remaining th_get_*() functions operate on modes and CRC values
and the like, and should be fine, remaining as ints.

Thanks very much to Magnus Holmgren for catching this behaviour.
https://lists.feep.net:8080/pipermail/libtar/2013-October/000365.html
---

diff --git a/lib/libtar.h b/lib/libtar.h
index 2fefee0..13bb82d 100644
--- a/lib/libtar.h
+++ b/lib/libtar.h
@@ -185,7 +185,11 @@ int th_write(TAR *t);
 
 /* decode tar header info */
 #define th_get_crc(t) oct_to_int((t)->th_buf.chksum)
-#define th_get_size(t) oct_to_int((t)->th_buf.size)
+/* We cast from int (what oct_to_int() returns) to
+   unsigned int, to avoid unwieldy sign extensions
+   from occurring on systems where size_t is bigger than int,
+   since th_get_size() is often stored into a size_t. */
+#define th_get_size(t) ((unsigned int)oct_to_int((t)->th_buf.size))
 #define th_get_mtime(t) oct_to_int((t)->th_buf.mtime)
 #define th_get_devmajor(t) oct_to_int((t)->th_buf.devmajor)
 #define th_get_devminor(t) oct_to_int((t)->th_buf.devminor)