From 2b2f42f9311ede75c3fe61d356094999e8e161b9 Mon Sep 17 00:00:00 2001
From: James Carter <jwcart2@gmail.com>
Date: Thu, 8 Apr 2021 13:24:29 -0400
Subject: [PATCH] libsepol/cil: Fix out-of-bound read of file context pattern
 ending with "\"

Based on patch by Nicolas Iooss, who writes:
  OSS-Fuzz found a Heap-buffer-overflow in the CIL compiler when trying
  to compile the following policy:

    (sid SID)
    (sidorder(SID))
    (filecon "\" any ())
    (filecon "" any ())

  When cil_post_fc_fill_data() processes "\", it goes beyond the NUL
  terminator of the string. Fix this by returning when '\0' is read
  after a backslash.

To be consistent with the function compute_diffdata() in
refpolicy/support/fc_sort.py, also increment str_len in this case.

Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=28484
Reported-by: Nicolas Iooss <nicolas.iooss@m4x.org>
Signed-off-by: James Carter <jwcart2@gmail.com>
---
 libsepol/cil/src/cil_post.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/libsepol/cil/src/cil_post.c b/libsepol/cil/src/cil_post.c
index 0b09cecc..bdeaa7c6 100644
--- a/libsepol/cil/src/cil_post.c
+++ b/libsepol/cil/src/cil_post.c
@@ -179,6 +179,13 @@ void cil_post_fc_fill_data(struct fc_data *fc, char *path)
 			break;
 		case '\\':
 			c++;
+			if (path[c] == '\0') {
+				if (!fc->meta) {
+					fc->stem_len++;
+				}
+				fc->str_len++;
+				return;
+			}
 			/* FALLTHRU */
 		default:
 			if (!fc->meta) {
-- 
2.30.2