On Tue, Aug 13, 2019 at 12:53:17PM +0100, Ben Hutchings wrote:
Denis Andzakovic discovered a potential use-after-free in older kernel versions, using syzkaller. tcp_write_queue_purge() frees all skbs in the TCP write queue and can leave sk->sk_send_head pointing to freed memory. tcp_disconnect() clears that pointer after calling tcp_write_queue_purge(), but tcp_connect() does not. It is (surprisingly) possible to add to the write queue between disconnection and reconnection, so this needs to be done in both places.
This bug was introduced by backports of commit 7f582b248d0a ("tcp: purge write queue in tcp_connect_init()") and does not exist upstream because of earlier changes in commit 75c119afe14f ("tcp: implement rb-tree based retransmit queue"). The latter is a major change that's not suitable for stable.
Reported-by: Denis Andzakovic denis.andzakovic@pulsesecurity.co.nz Bisected-by: Salvatore Bonaccorso carnil@debian.org Fixes: 7f582b248d0a ("tcp: purge write queue in tcp_connect_init()") Cc: stable@vger.kernel.org # before 4.15 Cc: Eric Dumazet edumazet@google.com Signed-off-by: Ben Hutchings ben@decadent.org.uk
include/net/tcp.h | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/include/net/tcp.h b/include/net/tcp.h index fed2a78fb8cb..f9b985d4d779 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1517,6 +1517,8 @@ struct tcp_fastopen_context { struct rcu_head rcu; }; +static inline void tcp_init_send_head(struct sock *sk);
/* write queue abstraction */ static inline void tcp_write_queue_purge(struct sock *sk) { @@ -1524,6 +1526,7 @@ static inline void tcp_write_queue_purge(struct sock *sk) while ((skb = __skb_dequeue(&sk->sk_write_queue)) != NULL) sk_wmem_free_skb(sk, skb);
- tcp_init_send_head(sk); sk_mem_reclaim(sk); tcp_clear_all_retrans_hints(tcp_sk(sk)); inet_csk(sk)->icsk_backoff = 0;
Nice catch, thanks for this. Now queued up everywhere.
greg k-h