[PATCH net v2] net: don't touch dev->stats in BPF redirect paths

[Jakub Kicinski <kuba@kernel.org>]

Gal reports that BPF redirect increments dev->stats.tx_errors
on failure. This is not correct, most modern drivers completely
ignore dev->stats so these drops will be invisible to the user.
Core code should use the dedicated core stats which are folded
into device stats in dev_get_stats().

Note that we're switching from tx_errors to tx_dropped.
Core only has tx_dropped, hence presumably users already expect
that counter to increment for "stack" Tx issues.

Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Reported-by: Gal Pressman <gal@nvidia.com>
Link: https://lore.kernel.org/c5df3b60-246a-4030-9c9a-0a35cd1ca924@nvidia.com
Fixes: b4ab31414970 ("bpf: Add redirect_neigh helper as redirect drop-in")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
v2:
 - add note on tx_dropped to the commit msg
v1: https://lore.kernel.org/20260128161030.39870-1-kuba@kernel.org

CC: ast@kernel.org
CC: eddyz87@gmail.com
CC: song@kernel.org
CC: yonghong.song@linux.dev
CC: john.fastabend@gmail.com
CC: kpsingh@kernel.org
CC: sdf@fomichev.me
CC: haoluo@google.com
CC: jolsa@kernel.org
CC: dsahern@gmail.com
CC: bpf@vger.kernel.org
---
 net/core/filter.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 616e0520a0bb..2c21735798a5 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2289,12 +2289,12 @@ static int __bpf_redirect_neigh_v6(struct sk_buff *skb, struct net_device *dev,
 
 	err = bpf_out_neigh_v6(net, skb, dev, nh);
 	if (unlikely(net_xmit_eval(err)))
-		DEV_STATS_INC(dev, tx_errors);
+		dev_core_stats_tx_dropped_inc(dev);
 	else
 		ret = NET_XMIT_SUCCESS;
 	goto out_xmit;
 out_drop:
-	DEV_STATS_INC(dev, tx_errors);
+	dev_core_stats_tx_dropped_inc(dev);
 	kfree_skb(skb);
 out_xmit:
 	return ret;
@@ -2396,12 +2396,12 @@ static int __bpf_redirect_neigh_v4(struct sk_buff *skb, struct net_device *dev,
 
 	err = bpf_out_neigh_v4(net, skb, dev, nh);
 	if (unlikely(net_xmit_eval(err)))
-		DEV_STATS_INC(dev, tx_errors);
+		dev_core_stats_tx_dropped_inc(dev);
 	else
 		ret = NET_XMIT_SUCCESS;
 	goto out_xmit;
 out_drop:
-	DEV_STATS_INC(dev, tx_errors);
+	dev_core_stats_tx_dropped_inc(dev);
 	kfree_skb(skb);
 out_xmit:
 	return ret;
-- 
2.52.0