drm: bridge: adv7511: unregister cec i2c device after cec adapter

CVE-2022-50412

What is CVE-2022-50412?

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

drm: bridge: adv7511: unregister cec i2c device after cec adapter

cec_unregister_adapter() assumes that the underlying adapter ops are callable. For example, if the CEC adapter currently has a valid physical address, then the unregistration procedure will invalidate the physical address by setting it to f.f.f.f. Whence the following kernel oops observed after removing the adv7511 module:

Unable to handle kernel execution of user memory at virtual address 0000000000000000
Internal error: Oops: 86000004 [#1] PREEMPT_RT SMP
Call trace:
 0x0
 adv7511_cec_adap_log_addr+0x1ac/0x1c8 [adv7511]
 cec_adap_unconfigure+0x44/0x90 [cec]
 __cec_s_phys_addr.part.0+0x68/0x230 [cec]
 __cec_s_phys_addr+0x40/0x50 [cec]
 cec_unregister_adapter+0xb4/0x118 [cec]
 adv7511_remove+0x60/0x90 [adv7511]
 i2c_device_remove+0x34/0xe0
 device_release_driver_internal+0x114/0x1f0
 driver_detach+0x54/0xe0
 bus_remove_driver+0x60/0xd8
 driver_unregister+0x34/0x60
 i2c_del_driver+0x2c/0x68
 adv7511_exit+0x1c/0x67c [adv7511]
 __arm64_sys_delete_module+0x154/0x288
 invoke_syscall+0x48/0x100
 el0_svc_common.constprop.0+0x48/0xe8
 do_el0_svc+0x28/0x88
 el0_svc+0x1c/0x50
 el0t_64_sync_handler+0xa8/0xb0
 el0t_64_sync+0x15c/0x160
Code: bad PC value
---[ end trace 0000000000000000 ]---

Protect against this scenario by unregistering i2c_cec after unregistering the CEC adapter. Duly disable the CEC clock afterwards too.

References