[PATCH net] net/sched: sch_cake: drop WARN_ON(1) for malformed packets in ACK filter

[PATCH net] net/sched: sch_cake: drop WARN_ON(1) for malformed packets in ACK filter

[Toke Høiland-Jørgensen]

The sch_cake ACK filter parses packets to find the TCP header and filter
duplicated ACKs if the flow is backlogged. The parsing code contains a
WARN_ON(1) which can be triggered by a malformed IP header in certain
cases. Depending on the system configuration, this leads either to
either spamming dmesg with warnings, or a panic if panic_on_warn is set.

The code already correctly skips the offending packet in the branch that
triggers the warning, so the WARN_ON itself doesn't really serve any
purpose. So just drop it altogether to avoid the inconvenient side
effects.

Fixes: 8b7138814f29 ("sch_cake: Add optional ACK filter")
Reported-by: Zhiling Zou <zhilinz@nebusec.ai>
Reported-by: Ren Wei <enjou1224z@gmail.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
---
 net/sched/sch_cake.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index f64be54ead49..f25f60978631 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1287,7 +1287,6 @@ static struct sk_buff *cake_ack_filter(struct cake_sched_data *q,
 
 			seglen = ipv6_payload_len(skb, ipv6h_check);
 		} else {
-			WARN_ON(1);  /* shouldn't happen */
 			continue;
 		}
 
-- 
2.55.0

Re: [PATCH net] net/sched: sch_cake: drop WARN_ON(1) for malformed packets in ACK filter

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 29 Jul 2026 21:14:16 +0200 you wrote:
> The sch_cake ACK filter parses packets to find the TCP header and filter
> duplicated ACKs if the flow is backlogged. The parsing code contains a
> WARN_ON(1) which can be triggered by a malformed IP header in certain
> cases. Depending on the system configuration, this leads either to
> either spamming dmesg with warnings, or a panic if panic_on_warn is set.
> 
> The code already correctly skips the offending packet in the branch that
> triggers the warning, so the WARN_ON itself doesn't really serve any
> purpose. So just drop it altogether to avoid the inconvenient side
> effects.
> 
> [...]

Here is the summary with links:
  - [net] net/sched: sch_cake: drop WARN_ON(1) for malformed packets in ACK filter
    https://git.kernel.org/netdev/net/c/2a33516f9ef5

You are awesome, thank you!
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