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openvswitch: only skb_tx_error() a packet we are about to drop

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queue_userspace_packet() borrows the packet skb -- it only copies it into
a private netlink message (user_skb) and does not own it; on return
do_execute_actions() keeps forwarding it through the flow's remaining
actions. Its error path nevertheless calls skb_tx_error(skb), which via
skb_zcopy_clear() does skb_shinfo(skb)->flags &= ~SKBFL_ALL_ZEROCOPY,
stripping SKBFL_SHARED_FRAG from that live skb (skb_tx_error()'s kerneldoc
says "skb must be freed afterwards").

For a MSG_ZEROCOPY skb carrying page-cache frags, SKBFL_SHARED_FRAG is
what makes esp_input() skb_cow_data() before in-place AEAD; once it is
stripped a later local ESP-in-UDP delivery decrypts in place over pages
the sender does not own -- an unprivileged page-cache write (the
"Fragnesia" primitive).
do_execute_actions() ignores output_userspace()'s return value, so any
action after a failed USERSPACE upcall inherits the stripped skb.

Move the skb_tx_error() to the flow-miss drop path - the "default"
branch of ovs_dp_process_packet()'s switch(error), before kfree_skb().

The call has been here since commit 36d5fe6a00 ("core, nfqueue,
openvswitch: Orphan frags in skb_zerocopy and handle errors") but was
harmless until esp_input() began relying on SKBFL_SHARED_FRAG to gate
in-place decrypt; only then did stripping it on a still-forwarded skb
become a page-cache write primitive.

Fixes: 36d5fe6a00 ("core, nfqueue, openvswitch: Orphan frags in skb_zerocopy and handle errors")
Fixes: f4c50a4034 ("xfrm: esp: avoid in-place decrypt on shared skb frags")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5
Signed-off-by: Norbert Szetei <norbert@doyensec.com>
Reviewed-by: Ilya Maximets <i.maximets@ovn.org>
Tested-by: Jongmin Jang <payload.jang@gmail.com>
Link: https://patch.msgid.link/55A52703-7548-4A55-A9CE-2A37145BDCAD@doyensec.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Norbert Szetei
2026-08-22 11:12:11 +02:00
committed by Paolo Abeni
parent b70b7b7156
commit 0dbc2398fc
1 changed files with 1 additions and 2 deletions
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3
net/openvswitch/datapath.c
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@@ -285,6 +285,7 @@ void ovs_dp_process_packet(struct sk_buff *skb, struct sw_flow_key *key)
consume_skb(skb);
break;
default:
skb_tx_error(skb);
kfree_skb(skb);
break;
}
@@ -604,8 +605,6 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb,
err = genlmsg_unicast(ovs_dp_get_net(dp), user_skb, upcall_info->portid);
user_skb = NULL;
out:
if (err)
skb_tx_error(skb);
consume_skb(user_skb);
consume_skb(nskb);