From: Masayuki Nakagawa Date: Wed, 24 Jan 2007 04:15:06 +0000 (-0800) Subject: [TCP]: skb is unexpectedly freed. X-Git-Tag: v2.6.20-rc6~5^2~8 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=fb7e2399ec17f1004c0e0ccfd17439f8759ede01;p=linux-2.6-omap-h63xx.git [TCP]: skb is unexpectedly freed. I encountered a kernel panic with my test program, which is a very simple IPv6 client-server program. The server side sets IPV6_RECVPKTINFO on a listening socket, and the client side just sends a message to the server. Then the kernel panic occurs on the server. (If you need the test program, please let me know. I can provide it.) This problem happens because a skb is forcibly freed in tcp_rcv_state_process(). When a socket in listening state(TCP_LISTEN) receives a syn packet, then tcp_v6_conn_request() will be called from tcp_rcv_state_process(). If the tcp_v6_conn_request() successfully returns, the skb would be discarded by __kfree_skb(). However, in case of a listening socket which was already set IPV6_RECVPKTINFO, an address of the skb will be stored in treq->pktopts and a ref count of the skb will be incremented in tcp_v6_conn_request(). But, even if the skb is still in use, the skb will be freed. Then someone still using the freed skb will cause the kernel panic. I suggest to use kfree_skb() instead of __kfree_skb(). Signed-off-by: Masayuki Nakagawa Signed-off-by: David S. Miller --- diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index c701f6abbfc..5c16e24a606 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4420,9 +4420,11 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, * But, this leaves one open to an easy denial of * service attack, and SYN cookies can't defend * against this problem. So, we drop the data - * in the interest of security over speed. + * in the interest of security over speed unless + * it's still in use. */ - goto discard; + kfree_skb(skb); + return 0; } goto discard;