blob: bb63da08c86c1c2dad6d90d8da6e974db8fde663
1 | /* vi: set sw=4 ts=4: */ |
2 | /* |
3 | * xreadlink.c - safe implementation of readlink. |
4 | * Returns a NULL on failure... |
5 | * |
6 | * Licensed under GPLv2, see file LICENSE in this source tree. |
7 | */ |
8 | |
9 | #include "libbb.h" |
10 | |
11 | /* some systems (eg Hurd) does not have MAXSYMLINKS definition, |
12 | * set it to some reasonable value if it isn't defined */ |
13 | #ifndef MAXSYMLINKS |
14 | # define MAXSYMLINKS 20 |
15 | #endif |
16 | |
17 | /* |
18 | * NOTE: This function returns a malloced char* that you will have to free |
19 | * yourself. |
20 | */ |
21 | char* FAST_FUNC xmalloc_readlink(const char *path) |
22 | { |
23 | enum { GROWBY = 80 }; /* how large we will grow strings by */ |
24 | |
25 | char *buf = NULL; |
26 | int bufsize = 0, readsize = 0; |
27 | |
28 | do { |
29 | bufsize += GROWBY; |
30 | buf = xrealloc(buf, bufsize); |
31 | readsize = readlink(path, buf, bufsize); |
32 | if (readsize == -1) { |
33 | free(buf); |
34 | return NULL; |
35 | } |
36 | } while (bufsize < readsize + 1); |
37 | |
38 | buf[readsize] = '\0'; |
39 | |
40 | return buf; |
41 | } |
42 | |
43 | /* |
44 | * This routine is not the same as realpath(), which |
45 | * canonicalizes the given path completely. This routine only |
46 | * follows trailing symlinks until a real file is reached and |
47 | * returns its name. If the path ends in a dangling link or if |
48 | * the target doesn't exist, the path is returned in any case. |
49 | * Intermediate symlinks in the path are not expanded -- only |
50 | * those at the tail. |
51 | * A malloced char* is returned, which must be freed by the caller. |
52 | */ |
53 | char* FAST_FUNC xmalloc_follow_symlinks(const char *path) |
54 | { |
55 | char *buf; |
56 | char *lpc; |
57 | char *linkpath; |
58 | int bufsize; |
59 | int looping = MAXSYMLINKS + 1; |
60 | |
61 | buf = xstrdup(path); |
62 | goto jump_in; |
63 | |
64 | while (1) { |
65 | linkpath = xmalloc_readlink(buf); |
66 | if (!linkpath) { |
67 | /* not a symlink, or doesn't exist */ |
68 | if (errno == EINVAL || errno == ENOENT) |
69 | return buf; |
70 | goto free_buf_ret_null; |
71 | } |
72 | |
73 | if (!--looping) { |
74 | free(linkpath); |
75 | free_buf_ret_null: |
76 | free(buf); |
77 | return NULL; |
78 | } |
79 | |
80 | if (*linkpath != '/') { |
81 | bufsize += strlen(linkpath); |
82 | buf = xrealloc(buf, bufsize); |
83 | lpc = bb_get_last_path_component_strip(buf); |
84 | strcpy(lpc, linkpath); |
85 | free(linkpath); |
86 | } else { |
87 | free(buf); |
88 | buf = linkpath; |
89 | jump_in: |
90 | bufsize = strlen(buf) + 1; |
91 | } |
92 | } |
93 | } |
94 | |
95 | char* FAST_FUNC xmalloc_readlink_or_warn(const char *path) |
96 | { |
97 | char *buf = xmalloc_readlink(path); |
98 | if (!buf) { |
99 | /* EINVAL => "file: Invalid argument" => puzzled user */ |
100 | const char *errmsg = "not a symlink"; |
101 | int err = errno; |
102 | if (err != EINVAL) |
103 | errmsg = strerror(err); |
104 | bb_error_msg("%s: cannot read link: %s", path, errmsg); |
105 | } |
106 | return buf; |
107 | } |
108 | |
109 | char* FAST_FUNC xmalloc_realpath(const char *path) |
110 | { |
111 | #if defined(__GLIBC__) || \ |
112 | (defined(__UCLIBC__) && UCLIBC_VERSION >= KERNEL_VERSION(0, 9, 31)) |
113 | /* glibc provides a non-standard extension */ |
114 | /* new: POSIX.1-2008 specifies this behavior as well */ |
115 | return realpath(path, NULL); |
116 | #else |
117 | char buf[PATH_MAX+1]; |
118 | |
119 | /* on error returns NULL (xstrdup(NULL) == NULL) */ |
120 | return xstrdup(realpath(path, buf)); |
121 | #endif |
122 | } |
123 |