Subject: CVE-2023-52856: drm/bridge: lt8912b: Fix crash on bridge detach

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

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

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

drm/bridge: lt8912b: Fix crash on bridge detach

The lt8912b driver, in its bridge detach function, calls
drm_connector_unregister() and drm_connector_cleanup().

drm_connector_unregister() should be called only for connectors
explicitly registered with drm_connector_register(), which is not the
case in lt8912b.

The driver's drm_connector_funcs.destroy hook is set to
drm_connector_cleanup().

Thus the driver should not call either drm_connector_unregister() nor
drm_connector_cleanup() in its lt8912_bridge_detach(), as they cause a
crash on bridge detach:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Mem abort info:
  ESR = 0x0000000096000006
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x06: level 2 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=00000000858f3000
[0000000000000000] pgd=0800000085918003, p4d=0800000085918003, pud=0800000085431003, pmd=0000000000000000
Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
Modules linked in: tidss(-) display_connector lontium_lt8912b tc358768 panel_lvds panel_simple drm_dma_helper drm_kms_helper drm drm_panel_orientation_quirks
CPU: 3 PID: 462 Comm: rmmod Tainted: G        W          6.5.0-rc2+ #2
Hardware name: Toradex Verdin AM62 on Verdin Development Board (DT)
pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : drm_connector_cleanup+0x78/0x2d4 [drm]
lr : lt8912_bridge_detach+0x54/0x6c [lontium_lt8912b]
sp : ffff800082ed3a90
x29: ffff800082ed3a90 x28: ffff0000040c1940 x27: 0000000000000000
x26: 0000000000000000 x25: dead000000000122 x24: dead000000000122
x23: dead000000000100 x22: ffff000003fb6388 x21: 0000000000000000
x20: 0000000000000000 x19: ffff000003fb6260 x18: fffffffffffe56e8
x17: 0000000000000000 x16: 0010000000000000 x15: 0000000000000038
x14: 0000000000000000 x13: ffff800081914b48 x12: 000000000000040e
x11: 000000000000015a x10: ffff80008196ebb8 x9 : ffff800081914b48
x8 : 00000000ffffefff x7 : ffff0000040c1940 x6 : ffff80007aa649d0
x5 : 0000000000000000 x4 : 0000000000000001 x3 : ffff80008159e008
x2 : 0000000000000000 x1 : 0000000000000000 x0 : 0000000000000000
Call trace:
 drm_connector_cleanup+0x78/0x2d4 [drm]
 lt8912_bridge_detach+0x54/0x6c [lontium_lt8912b]
 drm_bridge_detach+0x44/0x84 [drm]
 drm_encoder_cleanup+0x40/0xb8 [drm]
 drmm_encoder_alloc_release+0x1c/0x30 [drm]
 drm_managed_release+0xac/0x148 [drm]
 drm_dev_put.part.0+0x88/0xb8 [drm]
 devm_drm_dev_init_release+0x14/0x24 [drm]
 devm_action_release+0x14/0x20
 release_nodes+0x5c/0x90
 devres_release_all+0x8c/0xe0
 device_unbind_cleanup+0x18/0x68
 device_release_driver_internal+0x208/0x23c
 driver_detach+0x4c/0x94
 bus_remove_driver+0x70/0xf4
 driver_unregister+0x30/0x60
 platform_driver_unregister+0x14/0x20
 tidss_platform_driver_exit+0x18/0xb2c [tidss]
 __arm64_sys_delete_module+0x1a0/0x2b4
 invoke_syscall+0x48/0x110
 el0_svc_common.constprop.0+0x60/0x10c
 do_el0_svc_compat+0x1c/0x40
 el0_svc_compat+0x40/0xac
 el0t_32_sync_handler+0xb0/0x138
 el0t_32_sync+0x194/0x198
Code: 9104a276 f2fbd5b7 aa0203e1 91008af8 (f85c0420)

The Linux kernel CVE team has assigned CVE-2023-52856 to this issue.

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

	Issue introduced in 5.13 with commit 30e2ae943c26 and fixed in 5.15.139 with commit 42071feab712
	Issue introduced in 5.13 with commit 30e2ae943c26 and fixed in 6.1.63 with commit 7bf0cb8f4028
	Issue introduced in 5.13 with commit 30e2ae943c26 and fixed in 6.5.12 with commit fcd9895e3654
	Issue introduced in 5.13 with commit 30e2ae943c26 and fixed in 6.6.2 with commit b65e3249f3ca
	Issue introduced in 5.13 with commit 30e2ae943c26 and fixed in 6.7 with commit 44283993144a

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-2023-52856
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/lontium-lt8912b.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/42071feab712ba2a139b8928f7e0f8d3a6fc719e
	https://git.kernel.org/stable/c/7bf0cb8f40280a85034990dfe42be8ca8f80f37a
	https://git.kernel.org/stable/c/fcd9895e365474709844eeb31cfe53d912c3596e
	https://git.kernel.org/stable/c/b65e3249f3ca96e3c736af889461d80d675feab6
	https://git.kernel.org/stable/c/44283993144a03af9df31934d6c32bbd42d1a347