From: Eric Dumazet Date: Sat, 30 Apr 2022 01:15:23 +0000 (-0700) Subject: tcp: drop skb dst in tcp_rcv_established() X-Git-Tag: microblaze-v5.20~161^2~225 X-Git-Url: http://git.monstr.eu/?a=commitdiff_plain;h=783d108dd71d97e4cac5fe8ce70ca43ed7dc7bb7;p=linux-2.6-microblaze.git tcp: drop skb dst in tcp_rcv_established() In commit f84af32cbca7 ("net: ip_queue_rcv_skb() helper") I dropped the skb dst in tcp_data_queue(). This only dealt with so-called TCP input slow path. When fast path is taken, tcp_rcv_established() calls tcp_queue_rcv() while skb still has a dst. This was mostly fine, because most dsts at this point are not refcounted (thanks to early demux) However, TCP packets sent over loopback have refcounted dst. Then commit 68822bdf76f1 ("net: generalize skb freeing deferral to per-cpu lists") came and had the effect of delaying skb freeing for an arbitrary time. If during this time the involved netns is dismantled, cleanup_net() frees the struct net with embedded net->ipv6.ip6_dst_ops. Then when eventually dst_destroy_rcu() is called, if (dst->ops->destroy) ... triggers an use-after-free. It is not clear if ip6_route_net_exit() lacks a rcu_barrier() as syzbot reported similar issues before the blamed commit. ( https://groups.google.com/g/syzkaller-bugs/c/CofzW4eeA9A/m/009WjumTAAAJ ) Fixes: 68822bdf76f1 ("net: generalize skb freeing deferral to per-cpu lists") Signed-off-by: Eric Dumazet Acked-by: Neal Cardwell Acked-by: Soheil Hassas Yeganeh Signed-off-by: David S. Miller --- diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index cc3de8dc5797..97cfcd85f84e 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5928,6 +5928,7 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb) NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS); /* Bulk data transfer: receiver */ + skb_dst_drop(skb); __skb_pull(skb, tcp_header_len); eaten = tcp_queue_rcv(sk, skb, &fragstolen);