linux-kernel - Re: [PATCH v3] i2c: virtio: fix completion handling

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Message-ID: <20211203043917.z4njhql4y43tcbew@vireshk-i7>
Date:   Fri, 3 Dec 2021 10:09:17 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     wsa@...nel.org, Conghui Chen <conghui.chen@...el.com>,
        kernel@...s.com, Jie Deng <jie.deng@...el.com>,
        "Michael S. Tsirkin" <mst@...hat.com>, linux-i2c@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] i2c: virtio: fix completion handling

On 02-12-21, 16:32, Vincent Whitchurch wrote:
> The driver currently assumes that the notify callback is only received
> when the device is done with all the queued buffers.
> 
> However, this is not true, since the notify callback could be called
> without any of the queued buffers being completed (for example, with
> virtio-pci and shared interrupts) or with only some of the buffers being
> completed (since the driver makes them available to the device in
> multiple separate virtqueue_add_sgs() calls).
> 
> This can lead to incorrect data on the I2C bus or memory corruption in
> the guest if the device operates on buffers which are have been freed by
> the driver.  (The WARN_ON in the driver is also triggered.)
> 
>  BUG kmalloc-128 (Tainted: G        W        ): Poison overwritten
>  First byte 0x0 instead of 0x6b
>  Allocated in i2cdev_ioctl_rdwr+0x9d/0x1de age=243 cpu=0 pid=28
>  	memdup_user+0x2e/0xbd
>  	i2cdev_ioctl_rdwr+0x9d/0x1de
>  	i2cdev_ioctl+0x247/0x2ed
>  	vfs_ioctl+0x21/0x30
>  	sys_ioctl+0xb18/0xb41
>  Freed in i2cdev_ioctl_rdwr+0x1bb/0x1de age=68 cpu=0 pid=28
>  	kfree+0x1bd/0x1cc
>  	i2cdev_ioctl_rdwr+0x1bb/0x1de
>  	i2cdev_ioctl+0x247/0x2ed
>  	vfs_ioctl+0x21/0x30
>  	sys_ioctl+0xb18/0xb41
> 
> Fix this by calling virtio_get_buf() from the notify handler like other
> virtio drivers and by actually waiting for all the buffers to be
> completed.
> 
> Fixes: 3cfc88380413d20f ("i2c: virtio: add a virtio i2c frontend driver")
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
> ---
> 
> Notes:
>     v3: Wait for all completions instead of only the last one.

LGTM, thanks.

-- 
viresh