[DAPPER] x25: Prevent crashing when parsing bad X.25 facilities CVE-2010-4164

BugLink: http://bugs.launchpad.net/bugs/731199

CVE-2010-4164

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 <drosenberg@vsecurity.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
    (based on upstream commit 5ef41308f94dcbb3b7afc56cdef1c2ba53fa5d2f)
Signed-off-by: Steve Conklin <sconklin@canonical.com>
---
 net/x25/x25_facilities.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

On 03/08/2011 03:46 PM, Steve Conklin wrote:
> BugLink: http://bugs.launchpad.net/bugs/731199
>
> CVE-2010-4164
>
> 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<drosenberg@vsecurity.com>
> Signed-off-by: David S. Miller<davem@davemloft.net>
>      (based on upstream commit 5ef41308f94dcbb3b7afc56cdef1c2ba53fa5d2f)
> Signed-off-by: Steve Conklin<sconklin@canonical.com>
> ---
>   net/x25/x25_facilities.c |    8 ++++++++
>   1 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/net/x25/x25_facilities.c b/net/x25/x25_facilities.c
> index 54278b9..2af5e45 100644
> --- a/net/x25/x25_facilities.c
> +++ b/net/x25/x25_facilities.c
> @@ -43,6 +43,8 @@ int x25_parse_facilities(struct sk_buff *skb,
>   	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) {
> @@ -84,6 +86,8 @@ int x25_parse_facilities(struct sk_buff *skb,
>   			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];
> @@ -105,6 +109,8 @@ int x25_parse_facilities(struct sk_buff *skb,
>   			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]);
> @@ -112,6 +118,8 @@ int x25_parse_facilities(struct sk_buff *skb,
>   			len -= 4;
>   			break;
>   		case X25_FAC_CLASS_D:
> +			if (len<  p[1] + 2)
> +				return 0;
>   			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]);

Seems like you missed part of the upstream patch:

-					"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]);