+/*
+ * Make path appear as if a chroot had occurred:
+ * 1. remove leading "/" (or replace with "." if at end)
+ * 2. remove leading ".." components
+ * 3. delete any other "<dir>/.." (recursively)
+ * While we're at it, remove double slashes and "." components like
+ * clean_fname does(), but DON'T remove a trailing slash because that
+ * is sometimes significant on command line arguments.
+ * Can only shrink paths, so sanitizes in place.
+ * Contributed by Dave Dykstra <dwd@bell-labs.com>
+ */
+
+void sanitize_path(char *p)
+{
+ char *start, *sanp;
+
+ start = p;
+ sanp = p;
+ while (*p == '/') {
+ /* remove leading slashes */
+ p++;
+ }
+ while (*p != '\0') {
+ /* 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'))) {
+ /* skip "." component */
+ while (*++p == '/') {
+ /* skip following slashes */
+ ;
+ }
+ } else if ((*p == '.') && (*(p+1) == '.') &&
+ ((*(p+2) == '/') || (*(p+2) == '\0'))) {
+ /* skip ".." component followed by slash or end */
+ p += 2;
+ if (*p == '/')
+ p++;
+ if (sanp != start) {
+ /* back up sanp one level */
+ --sanp; /* now pointing at slash */
+ while ((sanp > start) && (*(sanp - 1) != '/')) {
+ /* skip back up to slash */
+ sanp--;
+ }
+ }
+ } else {
+ while (1) {
+ /* copy one component through next slash */
+ *sanp++ = *p++;
+ if ((*p == '\0') || (*(p-1) == '/')) {
+ while (*p == '/') {
+ /* skip multiple slashes */
+ p++;
+ }
+ break;
+ }
+ }
+ }
+ }
+ if (sanp == start) {
+ /* ended up with nothing, so put in "." component */
+ *sanp++ = '.';
+ }
+ *sanp = '\0';
+}
+