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d1fdcab7 PE |
1 | /* Read symbolic links into a buffer without size limitation, relative to fd. |
2 | ||
ab422c4d | 3 | Copyright (C) 2001, 2003-2004, 2007, 2009-2013 Free Software Foundation, |
d1fdcab7 PE |
4 | Inc. |
5 | ||
6 | This program is free software: you can redistribute it and/or modify | |
7 | it under the terms of the GNU General Public License as published by | |
8 | the Free Software Foundation; either version 3 of the License, or | |
9 | (at your option) any later version. | |
10 | ||
11 | This program is distributed in the hope that it will be useful, | |
12 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | GNU General Public License for more details. | |
15 | ||
16 | You should have received a copy of the GNU General Public License | |
17 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ | |
18 | ||
19 | /* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */ | |
20 | ||
21 | #include <config.h> | |
22 | ||
23 | #include "careadlinkat.h" | |
24 | ||
d1fdcab7 PE |
25 | #include <errno.h> |
26 | #include <limits.h> | |
d1fdcab7 | 27 | #include <string.h> |
d1fdcab7 | 28 | |
d1fdcab7 PE |
29 | /* Define this independently so that stdint.h is not a prerequisite. */ |
30 | #ifndef SIZE_MAX | |
31 | # define SIZE_MAX ((size_t) -1) | |
32 | #endif | |
33 | ||
34 | #ifndef SSIZE_MAX | |
35 | # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2)) | |
36 | #endif | |
37 | ||
69d9a57d PE |
38 | #include "allocator.h" |
39 | ||
d1fdcab7 PE |
40 | /* Assuming the current directory is FD, get the symbolic link value |
41 | of FILENAME as a null-terminated string and put it into a buffer. | |
42 | If FD is AT_FDCWD, FILENAME is interpreted relative to the current | |
43 | working directory, as in openat. | |
44 | ||
45 | If the link is small enough to fit into BUFFER put it there. | |
46 | BUFFER's size is BUFFER_SIZE, and BUFFER can be null | |
47 | if BUFFER_SIZE is zero. | |
48 | ||
49 | If the link is not small, put it into a dynamically allocated | |
50 | buffer managed by ALLOC. It is the caller's responsibility to free | |
51 | the returned value if it is nonnull and is not BUFFER. A null | |
52 | ALLOC stands for the standard allocator. | |
53 | ||
e5b28a7a PE |
54 | The PREADLINKAT function specifies how to read links. It operates |
55 | like POSIX readlinkat() | |
56 | <http://pubs.opengroup.org/onlinepubs/9699919799/functions/readlink.html> | |
57 | but can assume that its first argument is the same as FD. | |
d1fdcab7 PE |
58 | |
59 | If successful, return the buffer address; otherwise return NULL and | |
60 | set errno. */ | |
61 | ||
62 | char * | |
63 | careadlinkat (int fd, char const *filename, | |
64 | char *buffer, size_t buffer_size, | |
65 | struct allocator const *alloc, | |
66 | ssize_t (*preadlinkat) (int, char const *, char *, size_t)) | |
67 | { | |
68 | char *buf; | |
69 | size_t buf_size; | |
70 | size_t buf_size_max = | |
71 | SSIZE_MAX < SIZE_MAX ? (size_t) SSIZE_MAX + 1 : SIZE_MAX; | |
72 | char stack_buf[1024]; | |
73 | ||
9e0e57c7 | 74 | if (! alloc) |
7ec98caf | 75 | alloc = &stdlib_allocator; |
d1fdcab7 PE |
76 | |
77 | if (! buffer_size) | |
78 | { | |
79 | /* Allocate the initial buffer on the stack. This way, in the | |
80 | common case of a symlink of small size, we get away with a | |
81 | single small malloc() instead of a big malloc() followed by a | |
82 | shrinking realloc(). */ | |
83 | buffer = stack_buf; | |
84 | buffer_size = sizeof stack_buf; | |
85 | } | |
86 | ||
87 | buf = buffer; | |
88 | buf_size = buffer_size; | |
89 | ||
90 | do | |
91 | { | |
92 | /* Attempt to read the link into the current buffer. */ | |
93 | ssize_t link_length = preadlinkat (fd, filename, buf, buf_size); | |
94 | size_t link_size; | |
95 | if (link_length < 0) | |
96 | { | |
97 | /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1 | |
98 | with errno == ERANGE if the buffer is too small. */ | |
99 | int readlinkat_errno = errno; | |
100 | if (readlinkat_errno != ERANGE) | |
101 | { | |
102 | if (buf != buffer) | |
103 | { | |
9e0e57c7 | 104 | alloc->free (buf); |
d1fdcab7 PE |
105 | errno = readlinkat_errno; |
106 | } | |
107 | return NULL; | |
108 | } | |
109 | } | |
110 | ||
111 | link_size = link_length; | |
112 | ||
113 | if (link_size < buf_size) | |
114 | { | |
115 | buf[link_size++] = '\0'; | |
116 | ||
117 | if (buf == stack_buf) | |
118 | { | |
7ec98caf | 119 | char *b = (char *) alloc->allocate (link_size); |
f797625a | 120 | buf_size = link_size; |
d1fdcab7 PE |
121 | if (! b) |
122 | break; | |
123 | memcpy (b, buf, link_size); | |
124 | buf = b; | |
125 | } | |
7ec98caf | 126 | else if (link_size < buf_size && buf != buffer && alloc->reallocate) |
d1fdcab7 PE |
127 | { |
128 | /* Shrink BUF before returning it. */ | |
7ec98caf | 129 | char *b = (char *) alloc->reallocate (buf, link_size); |
d1fdcab7 PE |
130 | if (b) |
131 | buf = b; | |
132 | } | |
133 | ||
134 | return buf; | |
135 | } | |
136 | ||
137 | if (buf != buffer) | |
9e0e57c7 | 138 | alloc->free (buf); |
d1fdcab7 PE |
139 | |
140 | if (buf_size <= buf_size_max / 2) | |
141 | buf_size *= 2; | |
142 | else if (buf_size < buf_size_max) | |
143 | buf_size = buf_size_max; | |
f797625a PE |
144 | else if (buf_size_max < SIZE_MAX) |
145 | { | |
146 | errno = ENAMETOOLONG; | |
147 | return NULL; | |
148 | } | |
d1fdcab7 PE |
149 | else |
150 | break; | |
7ec98caf | 151 | buf = (char *) alloc->allocate (buf_size); |
d1fdcab7 PE |
152 | } |
153 | while (buf); | |
154 | ||
9e0e57c7 | 155 | if (alloc->die) |
f797625a | 156 | alloc->die (buf_size); |
d1fdcab7 PE |
157 | errno = ENOMEM; |
158 | return NULL; | |
159 | } |