Merge tag 'selinux-pr-20191007' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/selinux

Pull selinuxfix from Paul Moore:
 "One patch to ensure we don't copy bad memory up into userspace"

* tag 'selinux-pr-20191007' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/selinux:
  selinux: fix context string corruption in convert_context()

security/selinux/ss/services.c

@@ -1946,7 +1946,14 @@ static int convert_context(struct context *oldc, struct context *newc, void *p)
 		rc = string_to_context_struct(args->newp, NULL, s,
 					      newc, SECSID_NULL);
 		if (rc == -EINVAL) {
-			/* Retain string representation for later mapping. */
+			/*
+			 * Retain string representation for later mapping.
+			 *
+			 * IMPORTANT: We need to copy the contents of oldc->str
+			 * back into s again because string_to_context_struct()
+			 * may have garbled it.
+			 */
+			memcpy(s, oldc->str, oldc->len);
 			context_init(newc);
 			newc->str = s;
 			newc->len = oldc->len;