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d1fdcab7 PE |
1 | /* Read symbolic links into a buffer without size limitation, relative to fd. |
2 | ||
3 | Copyright (C) 2001, 2003-2004, 2007, 2009-2011 Free Software Foundation, | |
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 | ||
25 | #include "allocator.h" | |
26 | ||
27 | #include <errno.h> | |
28 | #include <limits.h> | |
29 | #include <stdlib.h> | |
30 | #include <string.h> | |
31 | #include <unistd.h> | |
32 | ||
33 | /* Use the system functions, not the gnulib overrides, because this | |
34 | module does not depend on GNU or POSIX semantics. */ | |
35 | #undef malloc | |
36 | #undef realloc | |
37 | ||
38 | /* Define this independently so that stdint.h is not a prerequisite. */ | |
39 | #ifndef SIZE_MAX | |
40 | # define SIZE_MAX ((size_t) -1) | |
41 | #endif | |
42 | ||
43 | #ifndef SSIZE_MAX | |
44 | # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2)) | |
45 | #endif | |
46 | ||
47 | #if ! HAVE_READLINKAT | |
48 | /* Ignore FD. Get the symbolic link value of FILENAME and put it into | |
49 | BUFFER, with size BUFFER_SIZE. This function acts like readlink | |
50 | but has readlinkat's signature. */ | |
51 | ssize_t | |
52 | careadlinkatcwd (int fd, char const *filename, char *buffer, | |
53 | size_t buffer_size) | |
54 | { | |
55 | (void) fd; | |
56 | return readlink (filename, buffer, buffer_size); | |
57 | } | |
58 | #endif | |
59 | ||
60 | /* Assuming the current directory is FD, get the symbolic link value | |
61 | of FILENAME as a null-terminated string and put it into a buffer. | |
62 | If FD is AT_FDCWD, FILENAME is interpreted relative to the current | |
63 | working directory, as in openat. | |
64 | ||
65 | If the link is small enough to fit into BUFFER put it there. | |
66 | BUFFER's size is BUFFER_SIZE, and BUFFER can be null | |
67 | if BUFFER_SIZE is zero. | |
68 | ||
69 | If the link is not small, put it into a dynamically allocated | |
70 | buffer managed by ALLOC. It is the caller's responsibility to free | |
71 | the returned value if it is nonnull and is not BUFFER. A null | |
72 | ALLOC stands for the standard allocator. | |
73 | ||
74 | The PREADLINKAT function specifies how to read links. | |
75 | ||
76 | If successful, return the buffer address; otherwise return NULL and | |
77 | set errno. */ | |
78 | ||
79 | char * | |
80 | careadlinkat (int fd, char const *filename, | |
81 | char *buffer, size_t buffer_size, | |
82 | struct allocator const *alloc, | |
83 | ssize_t (*preadlinkat) (int, char const *, char *, size_t)) | |
84 | { | |
85 | char *buf; | |
86 | size_t buf_size; | |
87 | size_t buf_size_max = | |
88 | SSIZE_MAX < SIZE_MAX ? (size_t) SSIZE_MAX + 1 : SIZE_MAX; | |
89 | char stack_buf[1024]; | |
90 | ||
91 | void *(*pmalloc) (size_t) = malloc; | |
92 | void *(*prealloc) (void *, size_t) = realloc; | |
93 | void (*pfree) (void *) = free; | |
94 | void (*pdie) (void) = NULL; | |
95 | if (alloc) | |
96 | { | |
97 | pmalloc = alloc->malloc; | |
98 | prealloc = alloc->realloc; | |
99 | pfree = alloc->free; | |
100 | pdie = alloc->die; | |
101 | } | |
102 | ||
103 | if (! buffer_size) | |
104 | { | |
105 | /* Allocate the initial buffer on the stack. This way, in the | |
106 | common case of a symlink of small size, we get away with a | |
107 | single small malloc() instead of a big malloc() followed by a | |
108 | shrinking realloc(). */ | |
109 | buffer = stack_buf; | |
110 | buffer_size = sizeof stack_buf; | |
111 | } | |
112 | ||
113 | buf = buffer; | |
114 | buf_size = buffer_size; | |
115 | ||
116 | do | |
117 | { | |
118 | /* Attempt to read the link into the current buffer. */ | |
119 | ssize_t link_length = preadlinkat (fd, filename, buf, buf_size); | |
120 | size_t link_size; | |
121 | if (link_length < 0) | |
122 | { | |
123 | /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1 | |
124 | with errno == ERANGE if the buffer is too small. */ | |
125 | int readlinkat_errno = errno; | |
126 | if (readlinkat_errno != ERANGE) | |
127 | { | |
128 | if (buf != buffer) | |
129 | { | |
130 | pfree (buf); | |
131 | errno = readlinkat_errno; | |
132 | } | |
133 | return NULL; | |
134 | } | |
135 | } | |
136 | ||
137 | link_size = link_length; | |
138 | ||
139 | if (link_size < buf_size) | |
140 | { | |
141 | buf[link_size++] = '\0'; | |
142 | ||
143 | if (buf == stack_buf) | |
144 | { | |
145 | char *b = (char *) pmalloc (link_size); | |
146 | if (! b) | |
147 | break; | |
148 | memcpy (b, buf, link_size); | |
149 | buf = b; | |
150 | } | |
151 | else if (link_size < buf_size && buf != buffer && prealloc) | |
152 | { | |
153 | /* Shrink BUF before returning it. */ | |
154 | char *b = (char *) prealloc (buf, link_size); | |
155 | if (b) | |
156 | buf = b; | |
157 | } | |
158 | ||
159 | return buf; | |
160 | } | |
161 | ||
162 | if (buf != buffer) | |
163 | pfree (buf); | |
164 | ||
165 | if (buf_size <= buf_size_max / 2) | |
166 | buf_size *= 2; | |
167 | else if (buf_size < buf_size_max) | |
168 | buf_size = buf_size_max; | |
169 | else | |
170 | break; | |
171 | buf = (char *) pmalloc (buf_size); | |
172 | } | |
173 | while (buf); | |
174 | ||
175 | if (pdie) | |
176 | pdie (); | |
177 | errno = ENOMEM; | |
178 | return NULL; | |
179 | } |