Hi, I have included this patch into my code and re-run our tests overnight, out of 644 iterations we did not see the kernel crash. Previous reproduction rate we would have expected 4-6 crashes in this time.
So I think this fixes the issue we are seeing. Thanks, Greg ________________________________________ From: netdev-ow...@vger.kernel.org <netdev-ow...@vger.kernel.org> on behalf of Eric Dumazet <eric.duma...@gmail.com> Sent: Saturday, 1 August 2015 10:14 p.m. To: Gregory Hoggarth Cc: Shawn Bohrer; netdev@vger.kernel.org; alexgartr...@gmail.com; Michal Kubeček Subject: [PATCH net] udp: fix dst races with multicast early demux From: Eric Dumazet <eduma...@google.com> Multicast dst are not cached. They carry DST_NOCACHE. As mentioned in commit f8864972126899 ("ipv4: fix dst race in sk_dst_get()"), these dst need special care before caching them into a socket. Caching them is allowed only if their refcnt was not 0, ie we must use atomic_inc_not_zero() Also, we must use READ_ONCE() to fetch sk->sk_rx_dst, as mentioned in commit d0c294c53a771 ("tcp: prevent fetching dst twice in early demux code") Fixes: 421b3885bf6d ("udp: ipv4: Add udp early demux") Signed-off-by: Eric Dumazet <eduma...@google.com> Reported-by: Gregory Hoggarth <gregory.hogga...@alliedtelesis.co.nz> Reported-by: Alex Gartrell <agartr...@fb.com> Cc: Michal Kubeček <mkube...@suse.cz> --- David : I will be on vacation for following 7 days, no internet access. Please wait for tests done by Gregory & Alex before merging this ? Thanks ! net/ipv4/udp.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 83aa604f9273..1b8c5ba7d5f7 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1995,12 +1995,19 @@ void udp_v4_early_demux(struct sk_buff *skb) skb->sk = sk; skb->destructor = sock_efree; - dst = sk->sk_rx_dst; + dst = READ_ONCE(sk->sk_rx_dst); if (dst) dst = dst_check(dst, 0); - if (dst) - skb_dst_set_noref(skb, dst); + if (dst) { + /* DST_NOCACHE can not be used without taking a reference */ + if (dst->flags & DST_NOCACHE) { + if (likely(atomic_inc_not_zero(&dst->__refcnt))) + skb_dst_set(skb, dst); + } else { + skb_dst_set_noref(skb, dst); + } + } } int udp_rcv(struct sk_buff *skb) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html