7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: yanxia [ Upstream commit c955325db639e9503941227e14e1f1ccc99442a1 ] veth_xdp_set() calculates the peer MTU limit from the incoming program's XDP fragment capability, but only stores it when no program was attached. Replacing a program with one having a different fragment capability therefore leaves the peer's max_mtu stale. Replacing a regular program with an xdp.frags program keeps rejecting otherwise valid jumbo MTUs. The opposite replacement leaves a larger limit in place and permits MTUs which a fresh attachment of the regular program would reject. Update peer->max_mtu after every successful attachment or replacement. Keep the GSO feature update conditional on the first attachment. Found during review of the XDP replacement path and confirmed with native XDP on an isolated veth pair. Before the fix, direct replacement rejects MTU 9000 after switching to xdp.frags, and accepts it after switching back to a regular program. Detaching and attaching instead produces the expected results in both directions. UML tests on net reproduce the problem before this change and match the detach/attach controls afterwards, with both devices up or down and with either endpoint receiving XDP. Failed replacements preserve the previous state; same-type replacements and detach also behave as expected. Small-frame traffic passes in the devices-up cases. Fixes: 7cda76d858a4 ("veth: Allow jumbo frames in xdp mode") Cc: stable@vger.kernel.org Signed-off-by: yanxia Link: https://patch.msgid.link/20261020020147.790274-1-yanxia@cmss.chinamobile.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- drivers/net/veth.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/net/veth.c b/drivers/net/veth.c index 643b97dc52456..7db389ae866dd 100644 --- a/drivers/net/veth.c +++ b/drivers/net/veth.c @@ -1622,10 +1622,9 @@ static int veth_xdp_set(struct net_device *dev, struct bpf_prog *prog, } } - if (!old_prog) { + if (!old_prog) peer->hw_features &= ~NETIF_F_GSO_SOFTWARE; - peer->max_mtu = max_mtu; - } + peer->max_mtu = max_mtu; xdp_features_set_redirect_target(peer, true); } -- 2.53.0