Re: [PATCH v2] wifi: cfg80211: Fix uninitialized header access in cfg80211_classify8021d

[Johannes Berg]

On Sat, 2025-11-08 at 00:03 +0530, Ranganath V N wrote:
> 
> +++ b/net/wireless/util.c
> @@ -963,9 +963,13 @@ unsigned int cfg80211_classify8021d(struct sk_buff *skb,
>  
>  	switch (skb->protocol) {
>  	case htons(ETH_P_IP):
> +		if (!pskb_may_pull(skb, sizeof(struct iphdr)))
> +			return 0;
>  		dscp = ipv4_get_dsfield(ip_hdr(skb)) & 0xfc;
>  		break;

That doesn't seem correct to me, passing only the IP header length to
pskb_may_pull() call assumes that ip_hdr(skb) == sbk->data, which is
almost certainly not true?

MPLS seems to not have this problem.

And maybe there's a similar issue for the VLAN tag?

johannes