netdev - Re: [PATCH net] rtnetlink: Refine sanity checks in rtnl_fdb

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Message-ID: <20181130145832.GA18412@splinter.mtl.com>
Date:   Fri, 30 Nov 2018 16:58:32 +0200
From:   Ido Schimmel <idosch@...sch.org>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        syzbot <syzkaller@...glegroups.com>,
        Ido Schimmel <idosch@...lanox.com>,
        David Ahern <dsahern@...il.com>
Subject: Re: [PATCH net] rtnetlink: Refine sanity checks in rtnl_fdb_{add|del}

On Fri, Nov 30, 2018 at 05:35:01AM -0800, 'Eric Dumazet' via syzkaller wrote:
> Commit da71577545a5 ("rtnetlink: Disallow FDB configuration
> for non-Ethernet device") added a test against dev->type.
> 
> kmsan was still able to trigger a kernel-infoleak using a gre device,
> with a correct device type (ARPHRD_ETHER), but with a not
> correct dev->addr_len (4 bytes instead of the expected 6 bytes)

Hi,

Can you please share the reproducer (assuming it exists)? I don't really
understand the fix. None of the functions you patched are in the trace.
Also, looking at IPv4 GRE code, while GRE device has dev->addr_len set
to 4, dev->type is set to ARPHRD_IPGRE.

Thanks