Subject: Re: [PATCH v2 net] net: ax25: fix integer overflow in ax25_rx_fragment()

From: David Laight <[email-masked]>
Date: Sun, 12 Apr 2026 22:05:50 +0100

On Sun, 12 Apr 2026 13:17:51 -0700
Jakub Kicinski <[email-masked]> wrote:

> On Thu,  9 Apr 2026 10:50:26 +0800 Mashiro Chen wrote:
> > Fix mirrors the identical bug fixed in NET/ROM (nr_in.c): check for
> > overflow before adding skb->len to fraglen, and abort fragment
> > reassembly cleanly if the limit would be exceeded.  
> 
> Same problem as reported by Simon on the netrom patch applies here.
> 
> nit: I don't think you need to cast ax25->fraglen to unsigned int
> in the comparison. since it's added with skb->len it should get
> auto-prompted to unsigned int.

It wouldn't matter if that comparison were signed.

Or change the type of ax25->fraglen to be 32bits and do the
sanity check for overlong packets later in the code.
I had a quick look at the header and the structure hasn't
been size-optimised...

	David