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