1 /* $OpenBSD: symlinks.c,v 1.7 2021/09/02 21:06:06 deraadt Exp $ */
2 /*
3 * Copyright (c) 2019 Kristaps Dzonsons <kristaps@bsd.lv>
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17
18 #include <assert.h>
19 #include <stdint.h>
20 #include <stdlib.h>
21 #include <limits.h>
22 #include <unistd.h>
23
24 #include "extern.h"
25
26 /*
27 * Allocate space for a readlink(2) invocation.
28 * Returns NULL on failure or a buffer otherwise.
29 * The buffer must be passed to free() by the caller.
30 */
31 char *
symlink_read(const char * path)32 symlink_read(const char *path)
33 {
34 char *buf = NULL;
35 size_t sz;
36 ssize_t nsz = 0;
37 void *pp;
38
39 for (sz = PATH_MAX; ; sz *= 2) {
40 if ((pp = realloc(buf, sz + 1)) == NULL) {
41 ERR("realloc");
42 free(buf);
43 return NULL;
44 }
45 buf = pp;
46
47 if ((nsz = readlink(path, buf, sz)) == -1) {
48 ERR("%s: readlink", path);
49 free(buf);
50 return NULL;
51 } else if (nsz == 0) {
52 ERRX("%s: empty link", path);
53 free(buf);
54 return NULL;
55 } else if ((size_t)nsz < sz)
56 break;
57 }
58
59 assert(buf != NULL);
60 assert(nsz > 0);
61 buf[nsz] = '\0';
62 return buf;
63 }
64
65 /*
66 * Allocate space for a readlinkat(2) invocation.
67 * Returns NULL on failure or a buffer otherwise.
68 * The buffer must be passed to free() by the caller.
69 */
70 char *
symlinkat_read(int fd,const char * path)71 symlinkat_read(int fd, const char *path)
72 {
73 char *buf = NULL;
74 size_t sz;
75 ssize_t nsz = 0;
76 void *pp;
77
78 for (sz = PATH_MAX; ; sz *= 2) {
79 if ((pp = realloc(buf, sz + 1)) == NULL) {
80 ERR("realloc");
81 free(buf);
82 return NULL;
83 }
84 buf = pp;
85
86 if ((nsz = readlinkat(fd, path, buf, sz)) == -1) {
87 ERR("%s: readlinkat", path);
88 free(buf);
89 return NULL;
90 } else if (nsz == 0) {
91 ERRX("%s: empty link", path);
92 free(buf);
93 return NULL;
94 } else if ((size_t)nsz < sz)
95 break;
96 }
97
98 assert(buf != NULL);
99 assert(nsz > 0);
100 buf[nsz] = '\0';
101 return buf;
102 }
103