Subject: CVE-2021-47613: i2c: virtio: fix completion handling

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

i2c: virtio: fix completion handling

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.

The Linux kernel CVE team has assigned CVE-2021-47613 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.15 with commit 3cfc88380413 and fixed in 5.15.10 with commit 9cbb957441ed
	Issue introduced in 5.15 with commit 3cfc88380413 and fixed in 5.16 with commit b503de239f62

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47613
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/i2c/busses/i2c-virtio.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/9cbb957441ed8873577d7d313a3d79d69f1dad5c
	https://git.kernel.org/stable/c/b503de239f62eca898cfb7e820d9a35499137d22