[3320] | 1 | /* vi: set sw=4 ts=4: */
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| 2 | /*
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| 3 | * xreadlink.c - safe implementation of readlink.
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| 4 | * Returns a NULL on failure...
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| 5 | *
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| 6 | * Licensed under GPLv2, see file LICENSE in this source tree.
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| 7 | */
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| 8 |
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| 9 | #include "libbb.h"
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| 10 |
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| 11 | /*
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| 12 | * NOTE: This function returns a malloced char* that you will have to free
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| 13 | * yourself.
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| 14 | */
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| 15 | char* FAST_FUNC xmalloc_readlink(const char *path)
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| 16 | {
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| 17 | enum { GROWBY = 80 }; /* how large we will grow strings by */
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| 18 |
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| 19 | char *buf = NULL;
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| 20 | int bufsize = 0, readsize = 0;
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| 21 |
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| 22 | do {
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| 23 | bufsize += GROWBY;
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| 24 | buf = xrealloc(buf, bufsize);
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| 25 | readsize = readlink(path, buf, bufsize);
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| 26 | if (readsize == -1) {
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| 27 | free(buf);
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| 28 | return NULL;
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| 29 | }
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| 30 | } while (bufsize < readsize + 1);
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| 31 |
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| 32 | buf[readsize] = '\0';
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| 33 |
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| 34 | return buf;
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| 35 | }
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| 36 |
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| 37 | /*
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| 38 | * This routine is not the same as realpath(), which
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| 39 | * canonicalizes the given path completely. This routine only
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| 40 | * follows trailing symlinks until a real file is reached and
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| 41 | * returns its name. If the path ends in a dangling link or if
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| 42 | * the target doesn't exist, the path is returned in any case.
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| 43 | * Intermediate symlinks in the path are not expanded -- only
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| 44 | * those at the tail.
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| 45 | * A malloced char* is returned, which must be freed by the caller.
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| 46 | */
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| 47 | char* FAST_FUNC xmalloc_follow_symlinks(const char *path)
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| 48 | {
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| 49 | char *buf;
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| 50 | char *lpc;
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| 51 | char *linkpath;
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| 52 | int bufsize;
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| 53 | int looping = MAXSYMLINKS + 1;
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| 54 |
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| 55 | buf = xstrdup(path);
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| 56 | goto jump_in;
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| 57 |
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| 58 | while (1) {
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| 59 | linkpath = xmalloc_readlink(buf);
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| 60 | if (!linkpath) {
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| 61 | /* not a symlink, or doesn't exist */
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| 62 | if (errno == EINVAL || errno == ENOENT)
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| 63 | return buf;
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| 64 | goto free_buf_ret_null;
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| 65 | }
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| 66 |
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| 67 | if (!--looping) {
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| 68 | free(linkpath);
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| 69 | free_buf_ret_null:
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| 70 | free(buf);
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| 71 | return NULL;
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| 72 | }
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| 73 |
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| 74 | if (*linkpath != '/') {
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| 75 | bufsize += strlen(linkpath);
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| 76 | buf = xrealloc(buf, bufsize);
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| 77 | lpc = bb_get_last_path_component_strip(buf);
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| 78 | strcpy(lpc, linkpath);
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| 79 | free(linkpath);
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| 80 | } else {
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| 81 | free(buf);
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| 82 | buf = linkpath;
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| 83 | jump_in:
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| 84 | bufsize = strlen(buf) + 1;
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| 85 | }
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| 86 | }
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| 87 | }
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| 88 |
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| 89 | char* FAST_FUNC xmalloc_readlink_or_warn(const char *path)
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| 90 | {
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| 91 | char *buf = xmalloc_readlink(path);
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| 92 | if (!buf) {
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| 93 | /* EINVAL => "file: Invalid argument" => puzzled user */
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| 94 | const char *errmsg = "not a symlink";
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| 95 | int err = errno;
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| 96 | if (err != EINVAL)
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| 97 | errmsg = strerror(err);
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| 98 | bb_error_msg("%s: cannot read link: %s", path, errmsg);
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| 99 | }
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| 100 | return buf;
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| 101 | }
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| 102 |
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| 103 | char* FAST_FUNC xmalloc_realpath(const char *path)
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| 104 | {
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| 105 | #if defined(__GLIBC__) && !defined(__UCLIBC__)
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| 106 | /* glibc provides a non-standard extension */
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| 107 | /* new: POSIX.1-2008 specifies this behavior as well */
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| 108 | return realpath(path, NULL);
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| 109 | #else
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| 110 | char buf[PATH_MAX+1];
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| 111 |
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| 112 | /* on error returns NULL (xstrdup(NULL) == NULL) */
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| 113 | return xstrdup(realpath(path, buf));
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| 114 | #endif
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| 115 | }
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