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https://github.com/topjohnwu/ndk-busybox.git
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105 lines
2.2 KiB
C
105 lines
2.2 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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#include "libbb.h"
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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. You have been warned.
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*/
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char *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 canonicalizes
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* the given path completely. this routine only follows trailing
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* symlinks until a real file is reached, and returns its name.
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* intermediate symlinks are not expanded. as above, a malloced
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* char* is returned, which must be freed.
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*/
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char *xmalloc_readlink_follow(const char *path)
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{
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char *buf = NULL, *lpc, *linkpath;
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int bufsize;
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smallint looping = 0;
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buf = strdup(path);
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bufsize = strlen(path) + 1;
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while(1) {
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linkpath = xmalloc_readlink(buf);
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if (!linkpath) {
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if (errno == EINVAL) /* not a symlink */
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return buf;
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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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free(buf);
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buf = linkpath;
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bufsize = strlen(linkpath) + 1;
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} else {
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bufsize += strlen(linkpath);
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if (looping++ > MAXSYMLINKS) {
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free(linkpath);
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free(buf);
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return NULL;
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}
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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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}
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}
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}
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char *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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bb_error_msg("%s: cannot read link (not a symlink?)", path);
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}
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return buf;
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}
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/* UNUSED */
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#if 0
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char *xmalloc_realpath(const char *path)
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{
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#if defined(__GLIBC__) && !defined(__UCLIBC__)
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/* glibc provides a non-standard extension */
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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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#endif
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