1/* Create /proc/self/fd-related names for subfiles of open directories.
2
3   Copyright (C) 2006, 2009-2010 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 <http://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 <string.h>
30#include <unistd.h>
31
32#include "dirname.h"
33#include "intprops.h"
34#include "same-inode.h"
35#include "xalloc.h"
36
37/* The results of open() in this file are not used with fchdir,
38   and we do not leak fds to any single-threaded code that could use stdio,
39   therefore save some unnecessary work in fchdir.c.
40   FIXME - if the kernel ever adds support for multi-thread safety for
41   avoiding standard fds, then we should use open_safer.  */
42#undef open
43#undef close
44
45#define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/%s"
46
47#define PROC_SELF_FD_NAME_SIZE_BOUND(len) \
48  (sizeof PROC_SELF_FD_FORMAT - sizeof "%d%s" \
49   + INT_STRLEN_BOUND (int) + (len) + 1)
50
51
52/* Set BUF to the expansion of PROC_SELF_FD_FORMAT, using FD and FILE
53   respectively for %d and %s.  If successful, return BUF if the
54   result fits in BUF, dynamically allocated memory otherwise.  But
55   return NULL if /proc is not reliable.  */
56char *
57openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file)
58{
59  static int proc_status = 0;
60
61  /* Make sure the caller gets ENOENT when appropriate.  */
62  if (!*file)
63    {
64      buf[0] = '\0';
65      return buf;
66    }
67
68  if (! proc_status)
69    {
70      /* Set PROC_STATUS to a positive value if /proc/self/fd is
71         reliable, and a negative value otherwise.  Solaris 10
72         /proc/self/fd mishandles "..", and any file name might expand
73         to ".." after symbolic link expansion, so avoid /proc/self/fd
74         if it mishandles "..".  Solaris 10 has openat, but this
75         problem is exhibited on code that built on Solaris 8 and
76         running on Solaris 10.  */
77
78      int proc_self_fd = open ("/proc/self/fd", O_RDONLY);
79      if (proc_self_fd < 0)
80        proc_status = -1;
81      else
82        {
83          struct stat proc_self_fd_dotdot_st;
84          struct stat proc_self_st;
85          char dotdot_buf[PROC_SELF_FD_NAME_SIZE_BOUND (sizeof ".." - 1)];
86          sprintf (dotdot_buf, PROC_SELF_FD_FORMAT, proc_self_fd, "..");
87          proc_status =
88            ((stat (dotdot_buf, &proc_self_fd_dotdot_st) == 0
89              && stat ("/proc/self", &proc_self_st) == 0
90              && SAME_INODE (proc_self_fd_dotdot_st, proc_self_st))
91             ? 1 : -1);
92          close (proc_self_fd);
93        }
94    }
95
96  if (proc_status < 0)
97    return NULL;
98  else
99    {
100      size_t bufsize = PROC_SELF_FD_NAME_SIZE_BOUND (strlen (file));
101      char *result = (bufsize < OPENAT_BUFFER_SIZE ? buf : xmalloc (bufsize));
102      sprintf (result, PROC_SELF_FD_FORMAT, fd, file);
103      return result;
104    }
105}
106