lib/openat-proc.c

   1 /* Create /proc/self/fd-related names for subfiles of open directories.
   2
   3    Copyright (C) 2006, 2009-2024 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation, either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Paul Eggert.  */
  19
  20 #include <config.h>
  21
  22 #include "openat-priv.h"
  23
  24 #include <sys/types.h>
  25 #include <sys/stat.h>
  26 #include <fcntl.h>
  27
  28 #include <stdio.h>
  29 #include <stdlib.h>
  30 #include <string.h>
  31 #include <unistd.h>
  32
  33 #ifdef __KLIBC__ /* OS/2 */
  34 # include <InnoTekLIBC/backend.h>
  35 #endif
  36 #ifdef __MVS__ /* z/OS */
  37 # include <termios.h>
  38 #endif
  39
  40 #include "intprops.h"
  41
  42 /* Set BUF to the name of the subfile of the directory identified by
  43    FD, where the subfile is named FILE.  If successful, return BUF if
  44    the result fits in BUF, dynamically allocated memory otherwise.
  45    Return NULL (setting errno) on error.  */
  46 char *
  47 openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file)
  48 {
  49   char *result = buf;
  50   int dirlen;
  51
  52   /* Make sure the caller gets ENOENT when appropriate.  */
  53   if (!*file)
  54     {
  55       buf[0] = '\0';
  56       return buf;
  57     }
  58
  59 #if !(defined __KLIBC__ || defined __MVS__)
  60   /* Generic code for Linux, Solaris, and similar platforms.  */
  61 # define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/"
  62   {
  63     enum {
  64       PROC_SELF_FD_DIR_SIZE_BOUND
  65         = (sizeof PROC_SELF_FD_FORMAT - (sizeof "%d" - 1)
  66            + INT_STRLEN_BOUND (int))
  67     };
  68
  69     static int proc_status = 0;
  70     if (! proc_status)
  71       {
  72         /* Set PROC_STATUS to a positive value if /proc/self/fd is
  73            reliable, and a negative value otherwise.  Solaris 10
  74            /proc/self/fd mishandles "..", and any file name might expand
  75            to ".." after symbolic link expansion, so avoid /proc/self/fd
  76            if it mishandles "..".  Solaris 10 has openat, but this
  77            problem is exhibited on code that built on Solaris 8 and
  78            running on Solaris 10.  */
  79
  80         int proc_self_fd =
  81           open ("/proc/self/fd",
  82                 O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK | O_CLOEXEC);
  83         if (proc_self_fd < 0)
  84           proc_status = -1;
  85         else
  86           {
  87             /* Detect whether /proc/self/fd/%i/../fd exists, where %i is the
  88                number of a file descriptor open on /proc/self/fd.  On Linux,
  89                that name resolves to /proc/self/fd, which was opened above.
  90                However, on Solaris, it may resolve to /proc/self/fd/fd, which
  91                cannot exist, since all names in /proc/self/fd are numeric.  */
  92             char dotdot_buf[PROC_SELF_FD_DIR_SIZE_BOUND + sizeof "../fd" - 1];
  93             sprintf (dotdot_buf, PROC_SELF_FD_FORMAT "../fd", proc_self_fd);
  94             proc_status = access (dotdot_buf, F_OK) ? -1 : 1;
  95             close (proc_self_fd);
  96           }
  97       }
  98
  99     if (proc_status < 0)
 100       return NULL;
 101     else
 102       {
 103         size_t bufsize = PROC_SELF_FD_DIR_SIZE_BOUND + strlen (file);
 104         if (OPENAT_BUFFER_SIZE < bufsize)
 105           {
 106             result = malloc (bufsize);
 107             if (! result)
 108               return NULL;
 109           }
 110
 111         dirlen = sprintf (result, PROC_SELF_FD_FORMAT, fd);
 112       }
 113   }
 114 #else /* (defined __KLIBC__ || defined __MVS__), i.e. OS/2 or z/OS */
 115   /* OS/2 kLIBC provides a function to retrieve a path from a fd.  */
 116   {
 117     size_t bufsize;
 118
 119 # ifdef __KLIBC__
 120     char dir[_MAX_PATH];
 121     if (__libc_Back_ioFHToPath (fd, dir, sizeof dir))
 122       return NULL;
 123 # endif
 124 # ifdef __MVS__
 125     char dir[_XOPEN_PATH_MAX];
 126     /* Documentation:
 127        https://www.ibm.com/docs/en/zos/2.2.0?topic=functions-w-ioctl-w-pioctl-control-devices */
 128     if (w_ioctl (fd, _IOCC_GPN, sizeof dir, dir) < 0)
 129       return NULL;
 130     /* Documentation:
 131        https://www.ibm.com/docs/en/zos/2.2.0?topic=functions-e2a-l-convert-characters-from-ebcdic-ascii */
 132     dirlen = __e2a_l (dir, strlen (dir));
 133     if (dirlen < 0 || dirlen >= sizeof dir)
 134       return NULL;
 135     dir[dirlen] = '\0';
 136 # endif
 137
 138     dirlen = strlen (dir);
 139     bufsize = dirlen + 1 + strlen (file) + 1; /* 1 for '/', 1 for null */
 140     if (OPENAT_BUFFER_SIZE < bufsize)
 141       {
 142         result = malloc (bufsize);
 143         if (! result)
 144           return NULL;
 145       }
 146
 147     strcpy (result, dir);
 148     result[dirlen++] = '/';
 149   }
 150 #endif
 151
 152   strcpy (result + dirlen, file);
 153   return result;
 154 }