Re: [PATCH net] bonding: avoid defaulting hard_header_len to ETH_HLEN on slave removal

[David Miller <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>]

From: Paolo Abeni <pabeni-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Date: Thu, 27 Apr 2017 19:29:34 +0200

> On slave list updates, the bonding driver computes its hard_header_len
> as the maximum of all enslaved devices's hard_header_len.
> If the slave list is empty, e.g. on last enslaved device removal,
> ETH_HLEN is used.
> 
> Since the bonding header_ops are set only when the first enslaved
> device is attached, the above can lead to header_ops->create()
> being called with the wrong skb headroom in place.
> 
> If bond0 is configured on top of ipoib devices, with the
> following commands:
> 
> ifup bond0
> for slave in $BOND_SLAVES_LIST; do
> 	ip link set dev $slave nomaster
> done
> ping -c 1 <ip on bond0 subnet>
> 
> we will obtain a skb_under_panic() with a similar call trace:
 ...
> This change addresses the issue avoiding updating the bonding device
> hard_header_len when the slaves list become empty, forbidding to
> shrink it below the value used by header_ops->create().
> 
> The bug is there since commit 54ef31371407 ("[PATCH] bonding: Handle large
> hard_header_len") but the panic can be triggered only since
> commit fc791b633515 ("IB/ipoib: move back IB LL address into the hard
> header").
> 
> Reported-by: Norbert P <noe-PRwTpj6vllL463JZfw7VRw@public.gmane.org>
> Fixes: 54ef31371407 ("[PATCH] bonding: Handle large hard_header_len")
> Fixes: fc791b633515 ("IB/ipoib: move back IB LL address into the hard header")
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Signed-off-by: Paolo Abeni <pabeni-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

Applied, thanks.
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