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)
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