1/* Create /proc/self/fd-related names for subfiles of open directories.
2
3   Copyright (C) 2006, 2009-2022 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__
34# include <InnoTekLIBC/backend.h>
35#endif
36
37#include "intprops.h"
38
39/* Set BUF to the name of the subfile of the directory identified by
40   FD, where the subfile is named FILE.  If successful, return BUF if
41   the result fits in BUF, dynamically allocated memory otherwise.
42   Return NULL (setting errno) on error.  */
43char *
44openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file)
45{
46  char *result = buf;
47  int dirlen;
48
49  /* Make sure the caller gets ENOENT when appropriate.  */
50  if (!*file)
51    {
52      buf[0] = '\0';
53      return buf;
54    }
55
56#ifndef __KLIBC__
57# define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/"
58  {
59    enum {
60      PROC_SELF_FD_DIR_SIZE_BOUND
61        = (sizeof PROC_SELF_FD_FORMAT - (sizeof "%d" - 1)
62           + INT_STRLEN_BOUND (int))
63    };
64
65    static int proc_status = 0;
66    if (! proc_status)
67      {
68        /* Set PROC_STATUS to a positive value if /proc/self/fd is
69           reliable, and a negative value otherwise.  Solaris 10
70           /proc/self/fd mishandles "..", and any file name might expand
71           to ".." after symbolic link expansion, so avoid /proc/self/fd
72           if it mishandles "..".  Solaris 10 has openat, but this
73           problem is exhibited on code that built on Solaris 8 and
74           running on Solaris 10.  */
75
76        int proc_self_fd =
77          open ("/proc/self/fd",
78                O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK | O_CLOEXEC);
79        if (proc_self_fd < 0)
80          proc_status = -1;
81        else
82          {
83            /* Detect whether /proc/self/fd/%i/../fd exists, where %i is the
84               number of a file descriptor open on /proc/self/fd.  On Linux,
85               that name resolves to /proc/self/fd, which was opened above.
86               However, on Solaris, it may resolve to /proc/self/fd/fd, which
87               cannot exist, since all names in /proc/self/fd are numeric.  */
88            char dotdot_buf[PROC_SELF_FD_DIR_SIZE_BOUND + sizeof "../fd" - 1];
89            sprintf (dotdot_buf, PROC_SELF_FD_FORMAT "../fd", proc_self_fd);
90            proc_status = access (dotdot_buf, F_OK) ? -1 : 1;
91            close (proc_self_fd);
92          }
93      }
94
95    if (proc_status < 0)
96      return NULL;
97    else
98      {
99        size_t bufsize = PROC_SELF_FD_DIR_SIZE_BOUND + strlen (file);
100        if (OPENAT_BUFFER_SIZE < bufsize)
101          {
102            result = malloc (bufsize);
103            if (! result)
104              return NULL;
105          }
106
107        dirlen = sprintf (result, PROC_SELF_FD_FORMAT, fd);
108      }
109  }
110#else
111  /* OS/2 kLIBC provides a function to retrieve a path from a fd.  */
112  {
113    char dir[_MAX_PATH];
114    size_t bufsize;
115
116    if (__libc_Back_ioFHToPath (fd, dir, sizeof dir))
117      return NULL;
118
119    dirlen = strlen (dir);
120    bufsize = dirlen + 1 + strlen (file) + 1; /* 1 for '/', 1 for null */
121    if (OPENAT_BUFFER_SIZE < bufsize)
122      {
123        result = malloc (bufsize);
124        if (! result)
125          return NULL;
126      }
127
128    strcpy (result, dir);
129    result[dirlen++] = '/';
130  }
131#endif
132
133  strcpy (result + dirlen, file);
134  return result;
135}
136