linux-kernel - Re: [v2 1/1] i2c: dev: prevent ZERO_SIZE_PTR deref in i2cdev_ioctl

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Message-ID: <20180427120658.wi32f7margtfazzp@ninjato>
Date:   Fri, 27 Apr 2018 14:06:58 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Alexander Popov <alex.popov@...ux.com>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, sil2review@...ts.osadl.org,
        Dmitry Vyukov <dvyukov@...gle.com>, syzkaller@...glegroups.com
Subject: Re: [v2 1/1] i2c: dev: prevent ZERO_SIZE_PTR deref in
 i2cdev_ioctl_rdwr()

On Thu, Apr 19, 2018 at 03:29:22PM +0300, Alexander Popov wrote:
> i2cdev_ioctl_rdwr() allocates i2c_msg.buf using memdup_user(), which
> returns ZERO_SIZE_PTR if i2c_msg.len is zero.
> 
> Currently i2cdev_ioctl_rdwr() always dereferences the buf pointer in case
> of I2C_M_RD | I2C_M_RECV_LEN transfer. That causes a kernel oops in
> case of zero len.
> 
> Let's check the len against zero before dereferencing buf pointer.
> 
> This issue was triggered by syzkaller.
> 
> Signed-off-by: Alexander Popov <alex.popov@...ux.com>

Applied to for-current with the arithmetic expression changed to '< 1'
to keep in sync with the previous one. Will push out soon, so you can
double check if you are interested.

Thanks for the debugging, Alexander!


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