1 /* Create /proc/self/fd-related names for subfiles of open directories.
2
3 Copyright (C) 2006, 2009-2023 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. */
43 char *
44 openat_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 }