busybox/libbb/xreadlink.c

/* 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 tarball for details.
 */

#include "libbb.h"

/*
 * 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)
{
#if defined(__GLIBC__) && !defined(__UCLIBC__)
	/* 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
}
1	niro	532	/* vi: set sw=4 ts=4: */
2			/*
3	niro	984	* xreadlink.c - safe implementation of readlink.
4			* Returns a NULL on failure...
5			*
6			* Licensed under GPLv2, see file LICENSE in this tarball for details.
7	niro	532	*/
8
9			#include "libbb.h"
10
11			/*
12			* NOTE: This function returns a malloced char* that you will have to free
13	niro	816	* yourself.
14	niro	532	*/
15	niro	816	char* FAST_FUNC xmalloc_readlink(const char *path)
16	niro	532	{
17			enum { GROWBY = 80 }; /* how large we will grow strings by */
18
19			char *buf = NULL;
20			int bufsize = 0, readsize = 0;
21
22			do {
23	niro	816	bufsize += GROWBY;
24			buf = xrealloc(buf, bufsize);
25			readsize = readlink(path, buf, bufsize);
26	niro	532	if (readsize == -1) {
27			free(buf);
28			return NULL;
29			}
30	niro	816	} while (bufsize < readsize + 1);
31	niro	532
32			buf[readsize] = '\0';
33
34			return buf;
35			}
36
37	niro	816	/*
38			* This routine is not the same as realpath(), which
39			* canonicalizes the given path completely. This routine only
40			* follows trailing symlinks until a real file is reached and
41			* returns its name. If the path ends in a dangling link or if
42			* the target doesn't exist, the path is returned in any case.
43			* Intermediate symlinks in the path are not expanded -- only
44			* those at the tail.
45			* A malloced char* is returned, which must be freed by the caller.
46			*/
47			char* FAST_FUNC xmalloc_follow_symlinks(const char *path)
48	niro	532	{
49	niro	816	char *buf;
50			char *lpc;
51			char *linkpath;
52			int bufsize;
53			int looping = MAXSYMLINKS + 1;
54
55			buf = xstrdup(path);
56			goto jump_in;
57
58			while (1) {
59			linkpath = xmalloc_readlink(buf);
60			if (!linkpath) {
61			/* not a symlink, or doesn't exist */
62			if (errno == EINVAL \|\| errno == ENOENT)
63			return buf;
64			goto free_buf_ret_null;
65			}
66
67			if (!--looping) {
68			free(linkpath);
69			free_buf_ret_null:
70			free(buf);
71			return NULL;
72			}
73
74			if (*linkpath != '/') {
75			bufsize += strlen(linkpath);
76			buf = xrealloc(buf, bufsize);
77			lpc = bb_get_last_path_component_strip(buf);
78			strcpy(lpc, linkpath);
79			free(linkpath);
80			} else {
81			free(buf);
82			buf = linkpath;
83			jump_in:
84			bufsize = strlen(buf) + 1;
85			}
86			}
87			}
88
89			char* FAST_FUNC xmalloc_readlink_or_warn(const char *path)
90			{
91			char *buf = xmalloc_readlink(path);
92			if (!buf) {
93			/* EINVAL => "file: Invalid argument" => puzzled user */
94	niro	984	const char *errmsg = "not a symlink";
95			int err = errno;
96			if (err != EINVAL)
97			errmsg = strerror(err);
98			bb_error_msg("%s: cannot read link: %s", path, errmsg);
99	niro	816	}
100			return buf;
101			}
102
103			char* FAST_FUNC xmalloc_realpath(const char *path)
104			{
105	niro	532	#if defined(__GLIBC__) && !defined(__UCLIBC__)
106			/* glibc provides a non-standard extension */
107	niro	1123	/* new: POSIX.1-2008 specifies this behavior as well */
108	niro	532	return realpath(path, NULL);
109			#else
110			char buf[PATH_MAX+1];
111
112	niro	1123	/* on error returns NULL (xstrdup(NULL) == NULL) */
113	niro	532	return xstrdup(realpath(path, buf));
114			#endif
115			}