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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