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8654f9d7 PE |
1 | /* Create /proc/self/fd-related names for subfiles of open directories. |
2 | ||
3 | Copyright (C) 2006, 2009-2013 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 <stdlib.h> | |
30 | #include <string.h> | |
31 | #include <unistd.h> | |
32 | ||
33 | #include "intprops.h" | |
34 | ||
35 | /* The results of open() in this file are not used with fchdir, | |
36 | and we do not leak fds to any single-threaded code that could use stdio, | |
37 | therefore save some unnecessary work in fchdir.c. | |
38 | FIXME - if the kernel ever adds support for multi-thread safety for | |
39 | avoiding standard fds, then we should use open_safer. */ | |
40 | #undef open | |
41 | #undef close | |
42 | ||
43 | #define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/%s" | |
44 | ||
45 | #define PROC_SELF_FD_NAME_SIZE_BOUND(len) \ | |
46 | (sizeof PROC_SELF_FD_FORMAT - sizeof "%d%s" \ | |
47 | + INT_STRLEN_BOUND (int) + (len) + 1) | |
48 | ||
49 | ||
50 | /* Set BUF to the expansion of PROC_SELF_FD_FORMAT, using FD and FILE | |
51 | respectively for %d and %s. If successful, return BUF if the | |
52 | result fits in BUF, dynamically allocated memory otherwise. But | |
53 | return NULL if /proc is not reliable, either because the operating | |
54 | system support is lacking or because memory is low. */ | |
55 | char * | |
56 | openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file) | |
57 | { | |
58 | static int proc_status = 0; | |
59 | ||
60 | /* Make sure the caller gets ENOENT when appropriate. */ | |
61 | if (!*file) | |
62 | { | |
63 | buf[0] = '\0'; | |
64 | return buf; | |
65 | } | |
66 | ||
67 | if (! proc_status) | |
68 | { | |
69 | /* Set PROC_STATUS to a positive value if /proc/self/fd is | |
70 | reliable, and a negative value otherwise. Solaris 10 | |
71 | /proc/self/fd mishandles "..", and any file name might expand | |
72 | to ".." after symbolic link expansion, so avoid /proc/self/fd | |
73 | if it mishandles "..". Solaris 10 has openat, but this | |
74 | problem is exhibited on code that built on Solaris 8 and | |
75 | running on Solaris 10. */ | |
76 | ||
77 | int proc_self_fd = open ("/proc/self/fd", | |
78 | O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK); | |
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_NAME_SIZE_BOUND (sizeof "../fd" - 1)]; | |
89 | sprintf (dotdot_buf, PROC_SELF_FD_FORMAT, proc_self_fd, "../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_NAME_SIZE_BOUND (strlen (file)); | |
100 | char *result = buf; | |
101 | if (OPENAT_BUFFER_SIZE < bufsize) | |
102 | { | |
103 | result = malloc (bufsize); | |
104 | if (! result) | |
105 | return NULL; | |
106 | } | |
107 | sprintf (result, PROC_SELF_FD_FORMAT, fd, file); | |
108 | return result; | |
109 | } | |
110 | } |