From: Guy Harris <guy@alum.mit.edu>
Date: Wed, 22 Oct 2014 19:31:21 +0000 (-0700)
Subject: Do bounds checking when unescaping PPP.
X-Git-Url: https://git.tcpdump.org/tcpdump/commitdiff_plain/1af0defd43415f15ccc26d14d8f79ff53c67d57c

Do bounds checking when unescaping PPP.

Clean up a const issue while we're at it.
---

diff --git a/print-ppp.c b/print-ppp.c
index ea8e00b2..c1eb4552 100644
--- a/print-ppp.c
+++ b/print-ppp.c
@@ -1266,11 +1266,15 @@ trunc:
 static void
 ppp_hdlc(const u_char *p, int length)
 {
-	u_char *b, *s, *t, c;
+	u_char *b, *t, c;
+	const u_char *s;
 	int i, proto;
 	const void *se;
 
-	b = (u_int8_t *)malloc(length);
+        if (length <= 0)
+                return;
+
+	b = (u_char *)malloc(length);
 	if (b == NULL)
 		return;
 
@@ -1279,14 +1283,13 @@ ppp_hdlc(const u_char *p, int length)
 	 * Do this so that we dont overwrite the original packet
 	 * contents.
 	 */
-	for (s = (u_char *)p, t = b, i = length; i > 0; i--) {
+	for (s = p, t = b, i = length; i > 0 && TTEST(*s); i--) {
 		c = *s++;
 		if (c == 0x7d) {
-			if (i > 1) {
-				i--;
-				c = *s++ ^ 0x20;
-			} else
-				continue;
+			if (i <= 1 || !TTEST(*s))
+				break;
+			i--;
+			c = *s++ ^ 0x20;
 		}
 		*t++ = c;
 	}