Multicast dst are not cached. They carry DST_NOCACHE.
As mentioned in commit f886497212 ("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 d0c294c53a ("tcp: prevent fetching dst twice in early demux
code")
Fixes: 421b3885bf ("udp: ipv4: Add udp early demux")
Tested-by: Gregory Hoggarth <Gregory.Hoggarth@alliedtelesis.co.nz>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Gregory Hoggarth <Gregory.Hoggarth@alliedtelesis.co.nz>
Reported-by: Alex Gartrell <agartrell@fb.com>
Cc: Michal Kubeček <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>
10e2eb878f