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authorPaul Moore <pmoore@redhat.com>2012-07-17 11:07:47 +0000
committerBen Hutchings <ben@decadent.org.uk>2012-08-19 18:15:23 +0100
commit7f6453d8c6f68e26fa6086c654b7fca39b960637 (patch)
treee1fb1e1454263ba79a943276c63b3b58f4754d48
parent9fbc36b812a7f55972682b4b175d2284f487df77 (diff)
downloadlwn-7f6453d8c6f68e26fa6086c654b7fca39b960637.tar.gz
lwn-7f6453d8c6f68e26fa6086c654b7fca39b960637.zip
cipso: don't follow a NULL pointer when setsockopt() is called
[ Upstream commit 89d7ae34cdda4195809a5a987f697a517a2a3177 ] 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> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
-rw-r--r--net/ipv4/cipso_ipv4.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index 86f3b885b4f3..afaa7351fd4b 100644
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -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;
}