busybox/libbb/xreadlink.c

/* vi: set sw=4 ts=4: */
/*
 *  xreadlink.c - safe implementation of readlink.
 *  Returns a NULL on failure...
 */

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