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cipso: don't follow a NULL pointer when setsockopt() is called

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As reported by Alan Cox, and verified by Lin Ming, when a user
attempts to add a CIPSO option to a socket using the CIPSO_V4_TAG_LOCAL
tag the kernel dies a terrible death when it attempts to follow a NULL
pointer (the skb argument to cipso_v4_validate() is NULL when called via
the setsockopt() syscall).

This patch fixes this by first checking to ensure that the skb is
non-NULL before using it to find the incoming network interface.  In
the unlikely case where the skb is NULL and the user attempts to add
a CIPSO option with the _TAG_LOCAL tag we return an error as this is
not something we want to allow.

A simple reproducer, kindly supplied by Lin Ming, although you must
have the CIPSO DOI #3 configure on the system first or you will be
caught early in cipso_v4_validate():

	#include <sys/types.h>
	#include <sys/socket.h>
	#include <linux/ip.h>
	#include <linux/in.h>
	#include <string.h>

	struct local_tag {
		char type;
		char length;
		char info[4];
	};

	struct cipso {
		char type;
		char length;
		char doi[4];
		struct local_tag local;
	};

	int main(int argc, char **argv)
	{
		int sockfd;
		struct cipso cipso = {
			.type = IPOPT_CIPSO,
			.length = sizeof(struct cipso),
			.local = {
				.type = 128,
				.length = sizeof(struct local_tag),
			},
		};

		memset(cipso.doi, 0, 4);
		cipso.doi[3] = 3;

		sockfd = socket(AF_INET, SOCK_DGRAM, 0);
		#define SOL_IP 0
		setsockopt(sockfd, SOL_IP, IP_OPTIONS,
			&cipso, sizeof(struct cipso));

		return 0;
	}

CC: Lin Ming <mlin@ss.pku.edu.cn>
Reported-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Paul Moore <pmoore@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paul Moore 2012-07-17 11:07:47 +00:00 committed by David S. Miller
parent a018540141
commit 89d7ae34cd
1 changed files with 4 additions and 2 deletions
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6
net/ipv4/cipso_ipv4.c
View File

@ -1725,8 +1725,10 @@ int cipso_v4_validate(const struct sk_buff *skb, unsigned char **option)
case CIPSO_V4_TAG_LOCAL:
/* This is a non-standard tag that we only allow for
* local connections, so if the incoming interface is
* not the loopback device drop the packet. */
if (!(skb->dev->flags & IFF_LOOPBACK)) {
* not the loopback device drop the packet. Further,
* there is no legitimate reason for setting this from
* userspace so reject it if skb is NULL. */
if (skb == NULL || !(skb->dev->flags & IFF_LOOPBACK)) {
err_offset = opt_iter;
goto validate_return_locked;
}