+/* Make path appear as if a chroot had occurred. This handles a leading
+ * "/" (either removing it or expanding it) and any leading or embedded
+ * ".." components that attempt to escape past the module's top dir.
+ *
+ * If dest is NULL, a buffer is allocated to hold the result. It is legal
+ * to call with the dest and the path (p) pointing to the same buffer, but
+ * rootdir will be ignored to avoid expansion of the string.
+ *
+ * The rootdir string contains a value to use in place of a leading slash.
+ * Specify NULL to get the default of "module_dir".
+ *
+ * The depth var is a count of how many '..'s to allow at the start of the
+ * path. If symlink is set, combine its value with the "p" value to get
+ * the target path, and **return NULL if any '..'s try to escape**.
+ *
+ * We also clean the path in a manner similar to clean_fname() but with a
+ * few differences:
+ *
+ * Turns multiple adjacent slashes into a single slash, gets rid of "." dir
+ * elements (INCLUDING a trailing dot dir), PRESERVES a trailing slash, and
+ * ALWAYS collapses ".." elements (except for those at the start of the
+ * string up to "depth" deep). If the resulting name would be empty,
+ * change it into a ".". */
+char *sanitize_path(char *dest, const char *p, const char *rootdir, int depth,
+ const char *symlink)
+{
+ char *start, *sanp, *save_dest = dest;
+ int rlen = 0, leave_one_dotdir = relative_paths;
+
+ if (symlink && *symlink == '/') {
+ p = symlink;
+ symlink = "";
+ }
+
+ if (dest != p) {
+ int plen = strlen(p);
+ if (*p == '/') {
+ if (!rootdir)
+ rootdir = module_dir;
+ rlen = strlen(rootdir);
+ depth = 0;
+ p++;
+ }
+ if (dest) {
+ if (rlen + plen + 1 >= MAXPATHLEN)
+ return NULL;
+ } else if (!(dest = new_array(char, rlen + plen + 1)))
+ out_of_memory("sanitize_path");
+ if (rlen) {
+ memcpy(dest, rootdir, rlen);
+ if (rlen > 1)
+ dest[rlen++] = '/';
+ }
+ }
+
+ start = sanp = dest + rlen;
+ while (1) {
+ if (*p == '\0') {
+ if (!symlink || !*symlink)
+ break;
+ while (sanp != start && sanp[-1] != '/') {
+ /* strip last element */
+ sanp--;
+ }
+ /* Append a relative symlink */
+ p = symlink;
+ symlink = "";
+ }
+ /* discard leading or extra slashes */
+ if (*p == '/') {
+ p++;
+ continue;
+ }
+ /* this loop iterates once per filename component in p.
+ * both p (and sanp if the original had a slash) should
+ * always be left pointing after a slash
+ */
+ if (*p == '.' && (p[1] == '/' || p[1] == '\0')) {
+ if (leave_one_dotdir && p[1])
+ leave_one_dotdir = 0;
+ else {
+ /* skip "." component */
+ p++;
+ continue;
+ }
+ }
+ if (*p == '.' && p[1] == '.' && (p[2] == '/' || p[2] == '\0')) {
+ /* ".." component followed by slash or end */
+ if (depth <= 0 || sanp != start) {
+ if (symlink && sanp == start) {
+ if (!save_dest)
+ free(dest);
+ return NULL;
+ }
+ p += 2;
+ if (sanp != start) {
+ /* back up sanp one level */
+ --sanp; /* now pointing at slash */
+ while (sanp > start && sanp[-1] != '/') {
+ /* skip back up to slash */
+ sanp--;
+ }
+ }
+ continue;
+ }
+ /* allow depth levels of .. at the beginning */
+ depth--;
+ /* move the virtual beginning to leave the .. alone */
+ start = sanp + 3;
+ }
+ /* copy one component through next slash */
+ while (*p && (*sanp++ = *p++) != '/') {}
+ }
+ if (sanp == dest) {
+ /* ended up with nothing, so put in "." component */
+ *sanp++ = '.';
+ }
+ *sanp = '\0';