CVE request: kernel: ipv6: skb is unexpectedly freed (remote DoS)

[Eugene Teo <eugeneteo () kernel sg>]

Upstream commit:
http://git.kernel.org/linus/fb7e2399ec17f1004c0e0ccfd17439f8759ede01

Description from the commit:
"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.

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."

Triggering this could result in a general protection fault.

Reference:
https://bugzilla.redhat.com/show_bug.cgi?id=577711

Thanks, Eugene