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;
}

/* UNUSED */
#if 0
char* FAST_FUNC xmalloc_realpath(const char *path)
{
#if defined(__GLIBC__) && !defined(__UCLIBC__)
	/* glibc provides a non-standard extension */
	return realpath(path, NULL);
#else
	char buf[PATH_MAX+1];

	/* on error returns NULL (xstrdup(NULL) ==NULL) */
	return xstrdup(realpath(path, buf));
#endif
}
#endif
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 tarball for details.
7	*/
8
9	#include "libbb.h"
10
11	/*
12	* NOTE: This function returns a malloced char* that you will have to free
13	* yourself.
14	*/
15	char* FAST_FUNC xmalloc_readlink(const char *path)
16	{
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	bufsize += GROWBY;
24	buf = xrealloc(buf, bufsize);
25	readsize = readlink(path, buf, bufsize);
26	if (readsize == -1) {
27	free(buf);
28	return NULL;
29	}
30	} while (bufsize < readsize + 1);
31
32	buf[readsize] = '\0';
33
34	return buf;
35	}
36
37	/*
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	{
49	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	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	}
100	return buf;
101	}
102
103	/* UNUSED */
104	#if 0
105	char* FAST_FUNC xmalloc_realpath(const char *path)
106	{
107	#if defined(__GLIBC__) && !defined(__UCLIBC__)
108	/* glibc provides a non-standard extension */
109	return realpath(path, NULL);
110	#else
111	char buf[PATH_MAX+1];
112
113	/* on error returns NULL (xstrdup(NULL) ==NULL) */
114	return xstrdup(realpath(path, buf));
115	#endif
116	}
117	#endif