[PATCH 1/6] libsepol/cil: fix out-of-bound read of a file context pattern ending with "\"

[Nicolas Iooss <nicolas.iooss@xxxxxxx>]

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.

Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=28484
Signed-off-by: Nicolas Iooss <nicolas.iooss@xxxxxxx>
---
 libsepol/cil/src/cil_post.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/libsepol/cil/src/cil_post.c b/libsepol/cil/src/cil_post.c
index a55df1ea5bb0..5f9cf4efd242 100644
--- a/libsepol/cil/src/cil_post.c
+++ b/libsepol/cil/src/cil_post.c
@@ -179,6 +179,12 @@ 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++;
+				}
+				return;
+			}
 			/* FALLTHRU */
 		default:
 			if (!fc->meta) {
-- 
2.30.2