Re: [PATCH net v2] ppp: reject claimed-as-LCP but actually malformed packets

On Tue, 2024-07-09 at 09:30 +0100, Simon Horman wrote:
> + Guillaume, Jakub
> 
> On Mon, Jul 08, 2024 at 02:56:15PM +0300, Dmitry Antipov wrote:
> > Since 'ppp_async_encode()' assumes valid LCP packets (with code
> > from 1 to 7 inclusive), add 'ppp_check_packet()' to ensure that
> > LCP packet has an actual body beyond PPP_LCP header bytes, and
> > reject claimed-as-LCP but actually malformed data otherwise.
> > 
> > Reported-by: [email protected]
> > Closes: https://syzkaller.appspot.com/bug?extid=ec0723ba9605678b14bf
> > Fixes: 44073187990d ("ppp: ensure minimum packet size in ppp_write()")
> 
> Sorry for not noticing this earlier.
> 
> I think that the cited commit is not where this problem was introduced.
> What that commit does is to introduce a length check.
> And what this patch does is to add another, more specific length check.
> But the problem fixed by this patch existed before the cited commit.
> 
> I expect that, like the cited commit, this patch:
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

No need to resend, I'll update the tag while applying the patch.

Thanks!

Paolo