From 2d02191779345b13de91048db441191b20264d16 Mon Sep 17 00:00:00 2001 From: Xia Yan Date: Thu, 29 Oct 2026 10:42:58 +0800 Subject: [PATCH] veth: keep carrier off when resizing channels with a down peer veth_set_channels() temporarily turns carrier off while reconfiguring a running interface. It then turns carrier on for both ends without checking whether the peer is administratively up. If only one end is up, changing its channel counts therefore reports LOWER_UP even though the peer remains down. For example, after creating a pair with two RX and TX queues per end: ip link set vca up ethtool -L vca rx 1 tx 1 vca incorrectly reports LOWER_UP while vcb is still down. Only restore carrier when the peer has IFF_UP, matching veth_open(). The local interface is already known to be running at this point. Found during LLM-assisted source review and reproduced with a veth pair in network namespaces, without kernel instrumentation or error injection. The companion veth.sh test reproduces the two mixed up/down failures before the fix and passes after it. Fixes: 4752eeb3d891 ("veth: implement support for set_channel ethtool op") Cc: stable@vger.kernel.org Reviewed-by: Hangbin Liu Signed-off-by: Xia Yan Reviewed-by: Jiayuan Chen Link: https://patch.msgid.link/20261029024259.3700-1-yana06070@163.com Signed-off-by: Paolo Abeni --- drivers/net/veth.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/net/veth.c b/drivers/net/veth.c index 3eca92d3dc60..a61842b2585b 100644 --- a/drivers/net/veth.c +++ b/drivers/net/veth.c @@ -1377,9 +1377,10 @@ static int veth_set_channels(struct net_device *dev, * to identify the range we have to disable */ veth_disable_range_safe(dev, new_rx_count, old_rx_count); - netif_carrier_on(dev); - if (peer) + if (peer && (peer->flags & IFF_UP)) { + netif_carrier_on(dev); netif_carrier_on(peer); + } } /* update XDP supported features */