[v2] libselinux: selinux_restorecon: fix realpath logic

Commit Message

Stephen Smalley Oct. 5, 2016, 2:59 p.m. UTC

The realpath logic in selinux_restorecon() was taken from the
Android libselinux fork.  However, bionic dirname() and basename()
do not modify their argument and therefore are safe to call on a
const string.  POSIX dirname() and basename() can modify their argument.
There is a GNU basename() that does not modify its argument, but not
for dirname().
For portability, create copies of the original pathname for each call
and keep them around until finished using the result.

Fixes "restorecon -r goes up the tree?" bug reported by Jason Zaman.

Reported-by: Jason Zaman <[e-mail]>
Signed-off-by: Stephen Smalley <[e-mail]>
---
v2 fixes some of the error paths and moves up the freeing of the
dirname_cpy to the earliest point possible.

 libselinux/src/selinux_restorecon.c | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

Patch

diff --git a/libselinux/src/selinux_restorecon.c b/libselinux/src/selinux_restorecon.c
index 0945138..e38d1d0 100644
--- a/libselinux/src/selinux_restorecon.c
+++ b/libselinux/src/selinux_restorecon.c
@@ -797,25 +797,41 @@  int selinux_restorecon(const char *pathname_orig,
 	 * realpath of containing dir, then appending last component name.
 	 */
 	if (flags.userealpath) {
-		pathbname = basename((char *)pathname_orig);
+		char *basename_cpy = strdup(pathname_orig);
+		if (!basename_cpy)
+			goto realpatherr;
+		pathbname = basename(basename_cpy);
 		if (!strcmp(pathbname, "/") || !strcmp(pathbname, ".") ||
 					    !strcmp(pathbname, "..")) {
 			pathname = realpath(pathname_orig, NULL);
-			if (!pathname)
+			if (!pathname) {
+				free(basename_cpy);
 				goto realpatherr;
+			}
 		} else {
-			pathdname = dirname((char *)pathname_orig);
+			char *dirname_cpy = strdup(pathname_orig);
+			if (!dirname_cpy) {
+				free(basename_cpy);
+				goto realpatherr;
+			}
+			pathdname = dirname(dirname_cpy);
 			pathdnamer = realpath(pathdname, NULL);
-			if (!pathdnamer)
+			free(dirname_cpy);
+			if (!pathdnamer) {
+				free(basename_cpy);
 				goto realpatherr;
+			}
 			if (!strcmp(pathdnamer, "/"))
 				error = asprintf(&pathname, "/%s", pathbname);
 			else
 				error = asprintf(&pathname, "%s/%s",
 						    pathdnamer, pathbname);
-			if (error < 0)
+			if (error < 0) {
+				free(basename_cpy);
 				goto oom;
+			}
 		}
+		free(basename_cpy);
 	} else {
 		pathname = strdup(pathname_orig);
 		if (!pathname)