linux-kernel - Re: [PATCH 4.19 01/51] ethtool: fix potential userspace buffer overflow

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Date:   Mon, 10 Jun 2019 10:21:12 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Vivien Didelot <vivien.didelot@...il.com>,
        Michal Kubecek <mkubecek@...e.cz>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 4.19 01/51] ethtool: fix potential userspace buffer
 overflow

Hi!

> From: Vivien Didelot <vivien.didelot@...il.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.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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