[PATCH] net: check qdisc_pkt_len_segs_init() return value on ingress

[PATCH] net: check qdisc_pkt_len_segs_init() return value on ingress

[David Carlier]

Commit 7fb4c1967011 ("net: pull headers in qdisc_pkt_len_segs_init()")
changed qdisc_pkt_len_segs_init() to return an skb drop reason when
it detects malicious GSO packets. The egress path in __dev_queue_xmit()
checks this return value and drops bad packets, but the ingress path in
sch_handle_ingress() ignores it.

This means malformed GSO packets entering via TC ingress are not dropped
and could be redirected to another interface or cause incorrect qdisc
accounting.

Check the return value and drop the packet when a bad GSO is detected.

Fixes: 7fb4c1967011 ("net: pull headers in qdisc_pkt_len_segs_init()")
Signed-off-by: David Carlier <devnexen@gmail.com>
---
 net/core/dev.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 5a31f9d2128c..2b5f508fc479 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4459,7 +4459,7 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret,
 		   struct net_device *orig_dev, bool *another)
 {
 	struct bpf_mprog_entry *entry = rcu_dereference_bh(skb->dev->tcx_ingress);
-	enum skb_drop_reason drop_reason = SKB_DROP_REASON_TC_INGRESS;
+	enum skb_drop_reason drop_reason;
 	struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
 	int sch_ret;
 
@@ -4472,7 +4472,15 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret,
 		*pt_prev = NULL;
 	}
 
-	qdisc_pkt_len_segs_init(skb);
+	drop_reason = qdisc_pkt_len_segs_init(skb);
+	if (unlikely(drop_reason)) {
+		kfree_skb_reason(skb, drop_reason);
+		*ret = NET_RX_DROP;
+		bpf_net_ctx_clear(bpf_net_ctx);
+		return NULL;
+	}
+
+	drop_reason = SKB_DROP_REASON_TC_INGRESS;
 	tcx_set_ingress(skb, true);
 
 	if (static_branch_unlikely(&tcx_needed_key)) {
-- 
2.53.0

Re: [PATCH] net: check qdisc_pkt_len_segs_init() return value on ingress

[Jakub Kicinski]

On Wed,  8 Apr 2026 18:23:07 +0100 David Carlier wrote:
> Commit 7fb4c1967011 ("net: pull headers in qdisc_pkt_len_segs_init()")
> changed qdisc_pkt_len_segs_init() to return an skb drop reason when
> it detects malicious GSO packets. The egress path in __dev_queue_xmit()
> checks this return value and drops bad packets, but the ingress path in
> sch_handle_ingress() ignores it.
> 
> This means malformed GSO packets entering via TC ingress are not dropped
> and could be redirected to another interface or cause incorrect qdisc
> accounting.
> 
> Check the return value and drop the packet when a bad GSO is detected.
> 
> Fixes: 7fb4c1967011 ("net: pull headers in qdisc_pkt_len_segs_init()")
> Signed-off-by: David Carlier <devnexen@gmail.com>

Not sure this can happen today, but okay.
Hopefully we won't get a patch for every Sashiko report we knowingly
ignored :|

> diff --git a/net/core/dev.c b/net/core/dev.c
> index 5a31f9d2128c..2b5f508fc479 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4459,7 +4459,7 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret,
>  		   struct net_device *orig_dev, bool *another)
>  {
>  	struct bpf_mprog_entry *entry = rcu_dereference_bh(skb->dev->tcx_ingress);
> -	enum skb_drop_reason drop_reason = SKB_DROP_REASON_TC_INGRESS;
> +	enum skb_drop_reason drop_reason;

this needs to move one line down now to keep the variable ordering.

>  	struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
>  	int sch_ret;
>  
> @@ -4472,7 +4472,15 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret,
>  		*pt_prev = NULL;
>  	}
>  
> -	qdisc_pkt_len_segs_init(skb);
> +	drop_reason = qdisc_pkt_len_segs_init(skb);
> +	if (unlikely(drop_reason)) {
> +		kfree_skb_reason(skb, drop_reason);
> +		*ret = NET_RX_DROP;
> +		bpf_net_ctx_clear(bpf_net_ctx);
> +		return NULL;
> +	}
> +
> +	drop_reason = SKB_DROP_REASON_TC_INGRESS;
>  	tcx_set_ingress(skb, true);
>  
>  	if (static_branch_unlikely(&tcx_needed_key)) {
-- 
pw-bot: cr