netdev - Re: [PATCH net] netfilter: check for out-of-bounds while copying compat entries

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Date:   Mon, 05 Mar 2018 16:17:36 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Florian Westphal <fw@...len.de>
Cc:     netdev@...r.kernel.org, Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        Stephen Hemminger <stephen@...workplumber.org>,
        netfilter-devel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH net] netfilter: check for out-of-bounds while copying
 compat entries

On Mon, 2018-03-05 at 15:32 +0100, Florian Westphal wrote:
> Paolo Abeni <pabeni@...hat.com> wrote:
> > Currently, when coping ebt compat entries, no checks are in place
> > for the offsets provided by user space, so that syzbot was able to
> > trigger the following splat:
> > ---
> >  net/bridge/netfilter/ebtables.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
> > index 02c4b409d317..54ceaff701fb 100644
> > --- a/net/bridge/netfilter/ebtables.c
> > +++ b/net/bridge/netfilter/ebtables.c
> > @@ -2114,7 +2114,7 @@ static int size_entry_mwt(struct ebt_entry *entry, const unsigned char *base,
> >  		unsigned int size;
> >  		char *buf = buf_start + offsets[i];
> >  
> > -		if (offsets[i] > offsets[j])
> > +		if (offsets[i] > offsets[j] || offsets[j] > *total)
> >  			return -EINVAL;
> 
> I thought i fixed this via b71812168571fa55e44cdd0254471331b9c4c4c6,
> and, after looking at it again I still don't see why that doesn't cover
> this :-(

Actually such commit fixes the issues (I just double-checked via
syzbot), the issue is I did not pull such changeset before starting
investigating this bug.

This patch is not needed, thanks.

Paolo