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Date: Thu, 29 Feb 2024 13:35:15 +0000
From: Lee Jones <lee@...nel.org>
To: linux-cve-announce@...r.kernel.org
Cc: Lee Jones <lee@...nel.org>
Subject: CVE-2024-26607: drm/bridge: sii902x: Fix probing race issue

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

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

drm/bridge: sii902x: Fix probing race issue

A null pointer dereference crash has been observed rarely on TI
platforms using sii9022 bridge:

[   53.271356]  sii902x_get_edid+0x34/0x70 [sii902x]
[   53.276066]  sii902x_bridge_get_edid+0x14/0x20 [sii902x]
[   53.281381]  drm_bridge_get_edid+0x20/0x34 [drm]
[   53.286305]  drm_bridge_connector_get_modes+0x8c/0xcc [drm_kms_helper]
[   53.292955]  drm_helper_probe_single_connector_modes+0x190/0x538 [drm_kms_helper]
[   53.300510]  drm_client_modeset_probe+0x1f0/0xbd4 [drm]
[   53.305958]  __drm_fb_helper_initial_config_and_unlock+0x50/0x510 [drm_kms_helper]
[   53.313611]  drm_fb_helper_initial_config+0x48/0x58 [drm_kms_helper]
[   53.320039]  drm_fbdev_dma_client_hotplug+0x84/0xd4 [drm_dma_helper]
[   53.326401]  drm_client_register+0x5c/0xa0 [drm]
[   53.331216]  drm_fbdev_dma_setup+0xc8/0x13c [drm_dma_helper]
[   53.336881]  tidss_probe+0x128/0x264 [tidss]
[   53.341174]  platform_probe+0x68/0xc4
[   53.344841]  really_probe+0x188/0x3c4
[   53.348501]  __driver_probe_device+0x7c/0x16c
[   53.352854]  driver_probe_device+0x3c/0x10c
[   53.357033]  __device_attach_driver+0xbc/0x158
[   53.361472]  bus_for_each_drv+0x88/0xe8
[   53.365303]  __device_attach+0xa0/0x1b4
[   53.369135]  device_initial_probe+0x14/0x20
[   53.373314]  bus_probe_device+0xb0/0xb4
[   53.377145]  deferred_probe_work_func+0xcc/0x124
[   53.381757]  process_one_work+0x1f0/0x518
[   53.385770]  worker_thread+0x1e8/0x3dc
[   53.389519]  kthread+0x11c/0x120
[   53.392750]  ret_from_fork+0x10/0x20

The issue here is as follows:

- tidss probes, but is deferred as sii902x is still missing.
- sii902x starts probing and enters sii902x_init().
- sii902x calls drm_bridge_add(). Now the sii902x bridge is ready from
  DRM's perspective.
- sii902x calls sii902x_audio_codec_init() and
  platform_device_register_data()
- The registration of the audio platform device causes probing of the
  deferred devices.
- tidss probes, which eventually causes sii902x_bridge_get_edid() to be
  called.
- sii902x_bridge_get_edid() tries to use the i2c to read the edid.
  However, the sii902x driver has not set up the i2c part yet, leading
  to the crash.

Fix this by moving the drm_bridge_add() to the end of the
sii902x_init(), which is also at the very end of sii902x_probe().

The Linux kernel CVE team has assigned CVE-2024-26607 to this issue.


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

	Issue introduced in 5.0 with commit 21d808405fe4 and fixed in 6.1.76 with commit e0f83c234ea7
	Issue introduced in 5.0 with commit 21d808405fe4 and fixed in 6.6.15 with commit 56f96cf6eb11
	Issue introduced in 5.0 with commit 21d808405fe4 and fixed in 6.7.3 with commit 2a4c6af7934a
	Issue introduced in 5.0 with commit 21d808405fe4 and fixed in 6.8-rc2 with commit 08ac6f132dd7

Please see https://www.kernel.org or 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-2024-26607
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/gpu/drm/bridge/sii902x.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/e0f83c234ea7a3dec1f84e5d02caa1c51664a076
	https://git.kernel.org/stable/c/56f96cf6eb11a1c2d594367c3becbfb06a855ec1
	https://git.kernel.org/stable/c/2a4c6af7934a7b4c304542c38fee35e09cc1770c
	https://git.kernel.org/stable/c/08ac6f132dd77e40f786d8af51140c96c6d739c9

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