netdev - Re: [PATCH] net: ethtool: avoid allocation failure for dump

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Message-Id: <20170118.114505.1855687422610394730.davem@davemloft.net>
Date:   Wed, 18 Jan 2017 11:45:05 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     darcari@...hat.com
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH] net: ethtool: avoid allocation failure for dump_regs

From: David Arcari <darcari@...hat.com>
Date: Wed, 18 Jan 2017 08:34:05 -0500

> If the user executes 'ethtool -d' for an interface and the associated
> get_regs_len() function returns 0, the user will see a call trace from
> the vmalloc() call in ethtool_get_regs().  This patch modifies
> ethtool_get_regs() to avoid the call to vmalloc when the size is zero.
> 
> Signed-off-by: David Arcari <darcari@...hat.com>

I think when the driver indicates this, it is equivalent to saying that
the operation isn't supported.

Also, this guards us against ->get_regs() methods that don't handle
zero length requests properly.  I see many which are going to do
really terrible things in that situation.

Therefore, if get_regs_len() returns zero, treat it the safe as if the
ethtool operations were NULL.

Thanks.