Add check in check_match for invalid match position.

1 files changed, 7 insertions, 0 deletions

diff --git a/deflate.c b/deflate.c
index 0d1d80c..f85bbb4 100644
--- a/deflate.c
+++ b/deflate.c
@@ -1201,6 +1201,13 @@ void check_match(deflate_state *s, Pos start, Pos match, int length) {
         fprintf(stderr, " start %u, match %u, length %d\n", start, match, length);
         z_error("invalid match length");
     }
+    /* check that the match isn't at the beginning of the window and that it isn't at
+     * the same position as the start string
+     */
+    if (match == 0 || match == start) {
+        fprintf(stderr, " start %u, match %u, length %d\n", start, match, length);
+        z_error("invalid match position");
+    }
     /* check that the match is indeed a match */
     if (memcmp(s->window + match, s->window + start, length) != EQUAL) {
         int32_t i = 0;