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

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Message-ID: <20180305143235.GK11889@breakpoint.cc>
Date:   Mon, 5 Mar 2018 15:32:35 +0100
From:   Florian Westphal <fw@...len.de>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        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

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 :-(