UPSTREAM: udp: consistently apply ufo or fragmentation

[ Upstream commit 85f1bd9a7b5a79d5baa8bf44af19658f7bf77bfa ]

When iteratively building a UDP datagram with MSG_MORE and that
datagram exceeds MTU, consistently choose UFO or fragmentation.

Once skb_is_gso, always apply ufo. Conversely, once a datagram is
split across multiple skbs, do not consider ufo.

Sendpage already maintains the first invariant, only add the second.
IPv6 does not have a sendpage implementation to modify.

A gso skb must have a partial checksum, do not follow sk_no_check_tx
in udp_send_skb.

Found by syzkaller.


Fixes: e89e9cf539a2 ("[IPv4/IPv6]: UFO Scatter-gather approach")
Reported-by: Andrey Konovalov <>
Signed-off-by: Willem de Bruijn <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>
(cherry picked from commit 938990d2433cdecd225e1ab54a442b3ffdce1f87)
Signed-off-by: Daniel Wang <>

Change-Id: I1809e6fb063d047622a6e34f7b0717b2195cfb1c
Tested-by: Daniel Wang <>
Reviewed-by: Guenter Roeck <>
Commit-Queue: Daniel Wang <>
3 files changed