[PATCH 6.12 096/113] net: gro: fix outer network offset

Greg Kroah-Hartman
2026-02-09T14:40:21Z

From: Paolo Abeni <pabeni@redhat.com>

[ Upstream commit 5c2c3c38be396257a6a2e55bd601a12bb9781507 ]

The udp GRO complete stage assumes that all the packets inserted the RX
have the `encapsulation` flag zeroed. Such assumption is not true, as a
few H/W NICs can set such flag when H/W offloading the checksum for
an UDP encapsulated traffic, the tun driver can inject GSO packets with
UDP encapsulation and the problematic layout can also be created via
a veth based setup.

Due to the above, in the problematic scenarios, udp4_gro_complete() uses
the wrong network offset (inner instead of outer) to compute the outer
UDP header pseudo checksum, leading to csum validation errors later on
in packet processing.

Address the issue always clearing the encapsulation flag at GRO completion
time. Such flag will be set again as needed for encapsulated packets by
udp_gro_complete().

Fixes: 5ef31ea5d053 ("net: gro: fix udp bad offset in socket lookup by adding {inner_}network_offset to napi_gro_cb")
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/562638dbebb3b15424220e26a180274b387e2a88.1770032084.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/core/gro.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/net/core/gro.c b/net/core/gro.c
index 0ad549b07e039..40aaac4e04f34 100644
--- a/net/core/gro.c
+++ b/net/core/gro.c
@@ -265,6 +265,8 @@ static void napi_gro_complete(struct napi_struct *napi, struct sk_buff *skb)
goto out;
}

+ /* NICs can feed encapsulated packets into GRO */
+ skb->encapsulation = 0;
rcu_read_lock();
list_for_each_entry_rcu(ptype, head, list) {
if (ptype->type != type || !ptype->callbacks.gro_complete)
--
2.51.0