From: Wei Wang <wei...@google.com>
Date: Fri, 10 Aug 2018 11:14:56 -0700
> From: Wei Wang <wei...@google.com>
>
> In l2tp code, if it is a L2TP_UDP_ENCAP tunnel, tunnel->sk points to a
> UDP socket. User could call sendmsg() on both this tunnel and the UDP
> socket itself concurrently. As l2tp_xmit_skb() holds socket lock and call
> __sk_dst_check() to refresh sk->sk_dst_cache, while udpv6_sendmsg() is
> lockless and call sk_dst_check() to refresh sk->sk_dst_cache, there
> could be a race and cause the dst cache to be freed multiple times.
> So we fix l2tp side code to always call sk_dst_check() to garantee
> xchg() is called when refreshing sk->sk_dst_cache to avoid race
> conditions.
>
> Syzkaller reported stack trace:
...
>
> Fixes: 71b1391a4128 ("l2tp: ensure sk->dst is still valid")
> Reported-by: syzbot+05f840f3b04f211ba...@syzkaller.appspotmail.com
> Signed-off-by: Wei Wang <wei...@google.com>
> Signed-off-by: Martin KaFai Lau <ka...@fb.com>
...
> ---
> v1->v2: Removed dst_clone() as Guillaume Nault suggested
Applied and queued up for -stable, thank you.
