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Date:   Mon, 10 Jun 2019 10:42:29 +0200
From:   Michal Kubecek <mkubecek@suse.cz>
To:     stable@vger.kernel.org
Cc:     Pavel Machek <pavel@denx.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org,
        Vivien Didelot <vivien.didelot@gmail.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH 4.19 01/51] ethtool: fix potential userspace buffer
 overflow
Message-ID: <20190610084229.GA31797@unicorn.suse.cz>
References: <20190609164127.123076536@linuxfoundation.org>
 <20190609164127.215699992@linuxfoundation.org>
 <20190610082112.GA8783@amd>
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On Mon, Jun 10, 2019 at 10:21:12AM +0200, Pavel Machek wrote:
> Hi!
> 
> > From: Vivien Didelot <vivien.didelot@gmail.com>
> > 
> > [ Upstream commit 0ee4e76937d69128a6a66861ba393ebdc2ffc8a2 ]
> > 
> > ethtool_get_regs() allocates a buffer of size ops->get_regs_len(),
> > and pass it to the kernel driver via ops->get_regs() for filling.
> > 
> > There is no restriction about what the kernel drivers can or cannot do
> > with the open ethtool_regs structure. They usually set regs->version
> > and ignore regs->len or set it to the same size as ops->get_regs_len().
> > 
> > But if userspace allocates a smaller buffer for the registers dump,
> > we would cause a userspace buffer overflow in the final copy_to_user()
> > call, which uses the regs.len value potentially reset by the driver.
> > 
> > To fix this, make this case obvious and store regs.len before calling
> > ops->get_regs(), to only copy as much data as requested by userspace,
> > up to the value returned by ops->get_regs_len().
> > 
> > While at it, remove the redundant check for non-null regbuf.
> 
> Mainline differs from 4.19-stable here, and while the non-null check
> is redundant in -mainline, it does not seem to be redundant in
> -stable.
> 
> In stable, if get_regs_len() returns < 0, we'll pass it to vzalloc.

Right. :-(

I guess we should also pick commit f9fc54d313fa ("ethtool: check the
return value of get_regs_len") to stable branches before 5.0.

Michal