[PATCH v2] Prevent crashing when parsing bad X.25 facilities

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.

v2 prevents printing values outside the appropriate range.

Signed-off-by: Dan Rosenberg <redacted>
CC: stable <stable@kernel.org>
---
 net/x25/x25_facilities.c |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/net/x25/x25_facilities.c b/net/x25/x25_facilities.c
index 3a8c4c4..7f18e7d 100644
--- a/net/x25/x25_facilities.c
+++ b/net/x25/x25_facilities.c

@@ -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 +157,8 @@ 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;

From: Dan Rosenberg <redacted>
Date: Fri, 12 Nov 2010 09:07:57 -0500

Thanks for not even compile testing your changes:

net/x25/x25_facilities.c: In function 'x25_parse_facilities':
net/x25/x25_facilities.c:161:6: error: expected ')' before 'p'
net/x25/x25_facilities.c:161:6: warning: too few arguments for format

I find this kind of carelessness extremely amusing coming from someone
who is so big on security theatre.

I find this kind of carelessness extremely amusing coming from someone
who is so big on security theatre.

You know what I find amusing?  The sheer number of security issues a
single person can find in his spare time.  Congratulations on your
attention to detail.

-Dan

From: Dan Rosenberg <redacted>
Date: Fri, 12 Nov 2010 15:44:25 -0500

quoted

I find this kind of carelessness extremely amusing coming from someone
who is so big on security theatre.

You know what I find amusing?  The sheer number of security issues a
single person can find in his spare time.  Congratulations on your
attention to detail.

I do not even agree that, for example, pointer exposure is a real
issue.  It still remains a matter of opinion.

And much of your claims and boasting is based upon that opinion.

So don't pass it off saliently or indirectly as fact.