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Prevent crashing when parsing bad X.25 facilities

PATCH Applied Dan Rosenberg 2 participants 2 messages Nov 12, 2010

Subsystems (3)
Networking Network drivers X.25 stack
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Dan Rosenberg

author
#0 lore raw

PATCH v3 1/1 Prevent crashing when parsing bad X.25 facilities

Now with improved comma support.

On parsing malformed X.25 facilities, decrementing the remaining length may cause it to underflow. Since the length is an unsigned integer, this will result in the loop continuing until the kernel crashes.

This patch adds checks to ensure decrementing the remaining length does not cause it to wrap around.

Signed-off-by Dan Rosenberg <[email protected]>
---
 net/x25/x25_facilities.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)
net/x25/x25_facilities.c +9 -3
index 3a8c4c4..55187c8 100644
@@ -61,6 +61,8 @@ int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
 	while (len > 0) {
 		switch (*p & X25_FAC_CLASS_MASK) {
 		case X25_FAC_CLASS_A:
+			if (len < 2)
+				return 0;
 			switch (*p) {
 			case X25_FAC_REVERSE:
 				if((p[1] & 0x81) == 0x81) {

@@ -104,6 +106,8 @@ int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
 			len -= 2;
 			break;
 		case X25_FAC_CLASS_B:
+			if (len < 3)
+				return 0;
 			switch (*p) {
 			case X25_FAC_PACKET_SIZE:
 				facilities->pacsize_in  = p[1];

@@ -125,6 +129,8 @@ int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
 			len -= 3;
 			break;
 		case X25_FAC_CLASS_C:
+			if (len < 4)
+				return 0;
 			printk(KERN_DEBUG "X.25: unknown facility %02X, "
 			       "values %02X, %02X, %02X\n",
 			       p[0], p[1], p[2], p[3]);

@@ -132,6 +138,8 @@ int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
 			len -= 4;
 			break;
 		case X25_FAC_CLASS_D:
+			if (len < p[1] + 2)
+				return 0;
 			switch (*p) {
 			case X25_FAC_CALLING_AE:
 				if (p[1] > X25_MAX_DTE_FACIL_LEN || p[1] <= 1)

@@ -149,9 +157,7 @@ int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
 				break;
 			default:
 				printk(KERN_DEBUG "X.25: unknown facility %02X,"
-					"length %d, values %02X, %02X, "
-					"%02X, %02X\n",
-					p[0], p[1], p[2], p[3], p[4], p[5]);
+					"length %d\n", p[0], p[1]);
 				break;
 			}
 			len -= p[1] + 2;
maintainer Applied
#1 lore raw

From: Dan Rosenberg <[email protected]>
Date: Fri, 12 Nov 2010 15:42:28 -0500

Quoted 10 lines

Now with improved comma support.

On parsing malformed X.25 facilities, decrementing the remaining length may cause it to underflow. Since the length is an unsigned integer, this will result in the loop continuing until the kernel crashes.

This patch adds checks to ensure decrementing the remaining length does not cause it to wrap around.

Signed-off-by Dan Rosenberg <[email protected]>

Applied.