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

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Date:   Fri, 30 Nov 2018 07:51:34 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Ido Schimmel <idosch@...sch.org>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        syzkaller@...glegroups.com, idosch@...lanox.com
Subject: Re: [PATCH net] rtnetlink: Refine sanity checks in rtnl_fdb_{add|del}

On Fri, Nov 30, 2018 at 7:46 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Fri, Nov 30, 2018 at 7:40 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Fri, Nov 30, 2018 at 7:36 AM David Ahern <dsahern@...il.com> wrote:
> > >
> > > On 11/30/18 7:58 AM, Ido Schimmel wrote:
> > > > 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.
> > >
> > > I had the same reaction ... you can not claim to be an ethernet device
> > > and have a hw address that is not 6 bytes.
> >
> > This has been discussed a number of times.... TUNSETLINK can do that.
> > (I have not checked what the repro does )
>
>
> Oh well...ndo_dflt_fdb_dump() seems to be used on a gre device.

What about :

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 54cfbda0b58be34dcb164028f17cdde2826c857b..b4cfc139c8b05b19564e02f29bd030c5ff85b51b
100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -3800,6 +3800,9 @@ int ndo_dflt_fdb_dump(struct sk_buff *skb,
 {
        int err;

+       if (dev->type != ARPHRD_ETHER || dev->addr_len != ETH_ALEN)
+               return -EINVAL;
+
        netif_addr_lock_bh(dev);
        err = nlmsg_populate_fdb(skb, cb, dev, idx, &dev->uc);
        if (err)