From: Masayuki Nakagawa Date: Fri, 2 Feb 2007 21:17:13 +0000 (-0800) Subject: [PATCH] TCP: skb is unexpectedly freed. X-Git-Tag: v2.6.19.3~5 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6e3e53bbff845b9c8d77967bf75bcd5325782199;p=thirdparty%2Fkernel%2Fstable.git [PATCH] 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 Signed-off-by: Chris Wright --- diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 026ef8f690fea..d71f42cdef93d 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4411,9 +4411,11 @@ 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;