Subject: Re: [PATCH v3 net] ax25: fix OOB read after address header strip in ax25_rcv()

From: David Laight <[email-masked]>
Date: Thu, 16 Apr 2026 10:21:37 +0100

On Wed, 15 Apr 2026 22:39:13 -0700 (PDT)
Ashutosh Desai <[email-masked]> wrote:

> On Wed, 15 Apr 2026 08:59:21 +0100, David Laight wrote:
> > Is it just worth linearising the skb on entry to all this code?  
> 
> Thanks for the feedback, David.
> 
> skb_linearize() on entry is a nice idea for simplifying sanity checks
> overall, but it wouldn't fix this particular bug on its own - the issue
> is skb->len dropping to zero after skb_pull(), not non-linear data. We'd
> still need a length check regardless. pskb_may_pull(skb, 2) handles both
> in one call.

The skb->len >= 2 check will be a lot cheaper/smaller.

> That said, linearizing on entry to ax25_rcv() as a cleanup to simplify
> future checks sounds worthwhile - happy to send that as a separate
> net-next patch.

I think you proposed just checking skb->len in an earlier version
and it was pointed out that the skb may not be linear.
So perhaps linearize as part of this fix and leave the simplifcation
of any other checks to later.

	David