155 lines
3.6 KiB
C
155 lines
3.6 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* xreadlink.c - safe implementation of readlink.
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* Returns a NULL on failure.
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*
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* Licensed under GPLv2, see file LICENSE in this source tree.
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*/
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#include "libbb.h"
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/* Some systems (eg Hurd) do not have MAXSYMLINKS definition,
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* set it to some reasonable value if it isn't defined */
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#ifndef MAXSYMLINKS
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# define MAXSYMLINKS 20
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#endif
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/*
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* NOTE: This function returns a malloced char* that you will have to free
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* yourself.
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*/
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char* FAST_FUNC xmalloc_readlink(const char *path)
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{
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enum { GROWBY = 80 }; /* how large we will grow strings by */
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char *buf = NULL;
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int bufsize = 0, readsize = 0;
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do {
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bufsize += GROWBY;
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buf = xrealloc(buf, bufsize);
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readsize = readlink(path, buf, bufsize);
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if (readsize == -1) {
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free(buf);
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return NULL;
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}
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} while (bufsize < readsize + 1);
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buf[readsize] = '\0';
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return buf;
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}
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/*
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* This routine is not the same as realpath(), which
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* canonicalizes the given path completely. This routine only
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* follows trailing symlinks until a real file is reached and
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* returns its name. If the path ends in a dangling link or if
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* the target doesn't exist, the path is returned in any case.
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* Intermediate symlinks in the path are not expanded -- only
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* those at the tail.
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* A malloced char* is returned, which must be freed by the caller.
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*/
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char* FAST_FUNC xmalloc_follow_symlinks(const char *path)
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{
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char *buf;
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char *lpc;
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char *linkpath;
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int bufsize;
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int looping = MAXSYMLINKS + 1;
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buf = xstrdup(path);
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goto jump_in;
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while (1) {
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linkpath = xmalloc_readlink(buf);
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if (!linkpath) {
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/* not a symlink, or doesn't exist */
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if (errno == EINVAL || errno == ENOENT)
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return buf;
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goto free_buf_ret_null;
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}
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if (!--looping) {
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free(linkpath);
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free_buf_ret_null:
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free(buf);
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return NULL;
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}
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if (*linkpath != '/') {
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bufsize += strlen(linkpath);
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buf = xrealloc(buf, bufsize);
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lpc = bb_get_last_path_component_strip(buf);
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strcpy(lpc, linkpath);
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free(linkpath);
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} else {
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free(buf);
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buf = linkpath;
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jump_in:
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bufsize = strlen(buf) + 1;
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}
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}
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}
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char* FAST_FUNC xmalloc_readlink_or_warn(const char *path)
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{
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char *buf = xmalloc_readlink(path);
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if (!buf) {
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/* EINVAL => "file: Invalid argument" => puzzled user */
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const char *errmsg = "not a symlink";
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int err = errno;
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if (err != EINVAL)
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errmsg = strerror(err);
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bb_error_msg("%s: cannot read link: %s", path, errmsg);
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}
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return buf;
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}
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char* FAST_FUNC xmalloc_realpath(const char *path)
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{
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/* NB: uclibc also defines __GLIBC__
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* Therefore the test "if glibc, or uclibc >= 0.9.31" looks a bit weird:
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*/
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#if defined(__GLIBC__) && \
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(!defined(__UCLIBC__) || UCLIBC_VERSION >= KERNEL_VERSION(0, 9, 31))
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/* glibc provides a non-standard extension */
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/* new: POSIX.1-2008 specifies this behavior as well */
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return realpath(path, NULL);
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#else
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char buf[PATH_MAX+1];
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/* on error returns NULL (xstrdup(NULL) == NULL) */
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return xstrdup(realpath(path, buf));
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#endif
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}
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char* FAST_FUNC xmalloc_realpath_coreutils(const char *path)
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{
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char *buf;
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errno = 0;
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buf = xmalloc_realpath(path);
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/*
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* There is one case when "readlink -f" and
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* "realpath" from coreutils succeed,
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* even though file does not exist, such as:
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* /tmp/file_does_not_exist
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* (the directory must exist).
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*/
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if (!buf && errno == ENOENT) {
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char *last_slash = strrchr(path, '/');
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if (last_slash) {
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*last_slash++ = '\0';
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buf = xmalloc_realpath(path);
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if (buf) {
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unsigned len = strlen(buf);
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buf = xrealloc(buf, len + strlen(last_slash) + 2);
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buf[len++] = '/';
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strcpy(buf + len, last_slash);
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}
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}
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}
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return buf;
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}
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