linux-kernel - Re: [PATCH v2] wifi: cfg80211: Fix uninitialized header access in cfg80211

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Message-ID: <f3a9797eb23d9c26007652798f14b76330aa1933.camel@sipsolutions.net>
Date: Mon, 10 Nov 2025 10:28:23 +0100
From: Johannes Berg <johannes@...solutions.net>
To: Ranganath V N <vnranganath.20@...il.com>, Dave Täht
	 <dave.taht@...ferbloat.net>, "John W. Linville" <linville@...driver.com>
Cc: linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org, 
	skhan@...uxfoundation.org, david.hunter.linux@...il.com, khalid@...nel.org,
 	syzbot+878ddc3962f792e9af59@...kaller.appspotmail.com
Subject: Re: [PATCH v2] wifi: cfg80211: Fix uninitialized header access in
 cfg80211_classify8021d

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