ND_TEST2 should validate that l is non-negative

diff --git a/netdissect.h b/netdissect.h
index b25f4c9fd5e79487f4d22e9858deb63b8f42bec3..7b8b5f4a1ecf382c24bee111052651a644a5fdca 100644 (file)
--- a/netdissect.h
+++ b/netdissect.h
@@ -271,8 +271,9 @@ struct netdissect_options {
  *     http://www.kb.cert.org/vuls/id/162289
  */
 #define ND_TTEST2(var, l) \
+  ((l) >= 0 && \
        ((uintptr_t)ndo->ndo_snapend - (l) <= (uintptr_t)ndo->ndo_snapend && \
-           (uintptr_t)&(var) <= (uintptr_t)ndo->ndo_snapend - (l))
+         (uintptr_t)&(var) <= (uintptr_t)ndo->ndo_snapend - (l)))
 
 /* True if "var" was captured */
 #define ND_TTEST(var) ND_TTEST2(var, sizeof(var))