From 32027e199368dad9508965aae8cd8de5b6ab5231 Mon Sep 17 00:00:00 2001

From: Guy Harris <guy@alum.mit.edu>

Date: Sat, 18 Apr 2020 14:04:59 -0700

Subject: [PATCH] PPP: When un-escaping, don't allocate a too-large buffer.

The buffer should be big enough to hold the captured data, but it

doesn't need to be big enough to hold the entire on-the-network packet,

if we haven't captured all of it.

(backported from commit e4add0b010ed6f2180dcb05a13026242ed935334)

---

 print-ppp.c | 18 ++++++++++++++----

 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/print-ppp.c b/print-ppp.c

index 891761728..33fb03412 100644

--- a/print-ppp.c

+++ b/print-ppp.c

@@ -1367,19 +1367,29 @@ print_bacp_config_options(netdissect_options *ndo,

 	return 0;

 }

+/*

+ * Un-escape RFC 1662 PPP in HDLC-like framing, with octet escapes.

+ * The length argument is the on-the-wire length, not the captured

+ * length; we can only un-escape the captured part.

+ */

 static void

 ppp_hdlc(netdissect_options *ndo,

          const u_char *p, int length)

 {

+	u_int caplen = ndo->ndo_snapend - p;

 	u_char *b, *t, c;

 	const u_char *s;

-	int i, proto;

+	u_int i;

+	int proto;

 	const void *se;

+	if (caplen == 0)

+		return;

+

         if (length <= 0)

                 return;

-	b = (u_char *)malloc(length);

+	b = (u_char *)malloc(caplen);

 	if (b == NULL)

 		return;

@@ -1388,10 +1398,10 @@ ppp_hdlc(netdissect_options *ndo,

 	 * Do this so that we dont overwrite the original packet

 	 * contents.

 	 */

-	for (s = p, t = b, i = length; i > 0 && ND_TTEST(*s); i--) {

+	for (s = p, t = b, i = caplen; i != 0; i--) {

 		c = *s++;

 		if (c == 0x7d) {

-			if (i <= 1 || !ND_TTEST(*s))

+			if (i <= 1)

 				break;

 			i--;

 			c = *s++ ^ 0x20;