ZDI reported and analyzed a race condition during close for espintcp sockets: espintcp_close() frees emsg->skb via kfree_skb() without holding any socket lock. Concurrently, the xfrm_trans_reinject work queue invokes esp_output_tcp_finish() -> espintcp_push_skb() -> espintcp_push_msgs() -> skb_send_sock_locked(), which reads the same skb as a data source. Fix this by adding a synchronize_rcu() call after resetting sk_prot, since esp_output_tcp_finish() runs under RCU and won't use a socket with sk_prot == &tcp_prot. Simply taking the socket lock in espintcp_close() could lead to leaks, if esp_output_tcp_finish() re-adds an skb in the slot we just freed. After this, the existing barrier() is no longer needed. Cc: stable@vger.kernel.org Fixes: e27cca96cd68 ("xfrm: add espintcp (RFC 8229)") Reported-by: zdi-disclosures@trendmicro.com Signed-off-by: Sabrina Dubroca --- v2: remove the unnecessary barrier() v1: https://lore.kernel.org/netdev/50e2ab4348eb8177581058f0152394cfae6a8d27.1783071494.git.sd@queasysnail.net/ net/xfrm/espintcp.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/xfrm/espintcp.c b/net/xfrm/espintcp.c index 374e1b964438..cd817b855ba1 100644 --- a/net/xfrm/espintcp.c +++ b/net/xfrm/espintcp.c @@ -515,7 +515,8 @@ static void espintcp_close(struct sock *sk, long timeout) strp_stop(&ctx->strp); sk->sk_prot = &tcp_prot; - barrier(); + + synchronize_rcu(); disable_work_sync(&ctx->work); strp_done(&ctx->strp); -- 2.54.0