drm/meson: remove drm bridges at aggregate driver unbind time
CVE: CVE-2022-50256
Component: kernel
Severity: None
Release date: 2022-01-01T00:00:00+00:00

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

drm/meson: remove drm bridges at aggregate driver unbind time

drm bridges added by meson_encoder_hdmi_init and meson_encoder_cvbs_init
were not manually removed at module unload time, which caused dangling
references to freed memory to remain linked in the global bridge_list.

When loading the driver modules back in, the same functions would again
call drm_bridge_add, and when traversing the global bridge_list, would
end up peeking into freed memory.

Once again KASAN revealed the problem:

[  +0.000095] =============================================================
[  +0.000008] BUG: KASAN: use-after-free in __list_add_valid+0x9c/0x120
[  +0.000018] Read of size 8 at addr ffff00003da291f0 by task modprobe/2483

[  +0.000018] CPU: 3 PID: 2483 Comm: modprobe Tainted: G         C O      5.19.0-rc6-lrmbkasan+ #1
[  +0.000011] Hardware name: Hardkernel ODROID-N2Plus (DT)
[  +0.000008] Call trace:
[  +0.000006]  dump_backtrace+0x1ec/0x280
[  +0.000012]  show_stack+0x24/0x80
[  +0.000008]  dump_stack_lvl+0x98/0xd4
[  +0.000011]  print_address_description.constprop.0+0x80/0x520
[  +0.000011]  print_report+0x128/0x260
[  +0.000008]  kasan_report+0xb8/0xfc
[  +0.000008]  __asan_report_load8_noabort+0x3c/0x50
[  +0.000009]  __list_add_valid+0x9c/0x120
[  +0.000009]  drm_bridge_add+0x6c/0x104 [drm]
[  +0.000165]  dw_hdmi_probe+0x1900/0x2360 [dw_hdmi]
[  +0.000022]  meson_dw_hdmi_bind+0x520/0x814 [meson_dw_hdmi]
[  +0.000014]  component_bind+0x174/0x520
[  +0.000012]  component_bind_all+0x1a8/0x38c
[  +0.000010]  meson_drv_bind_master+0x5e8/0xb74 [meson_drm]
[  +0.000032]  meson_drv_bind+0x20/0x2c [meson_drm]
[  +0.000027]  try_to_bring_up_aggregate_device+0x19c/0x390
[  +0.000010]  component_master_add_with_match+0x1c8/0x284
[  +0.000009]  meson_drv_probe+0x274/0x280 [meson_drm]
[  +0.000026]  platform_probe+0xd0/0x220
[  +0.000009]  really_probe+0x3ac/0xa80
[  +0.000009]  __driver_probe_device+0x1f8/0x400
[  +0.000009]  driver_probe_device+0x68/0x1b0
[  +0.000009]  __driver_attach+0x20c/0x480
[  +0.000008]  bus_for_each_dev+0x114/0x1b0
[  +0.000009]  driver_attach+0x48/0x64
[  +0.000008]  bus_add_driver+0x390/0x564
[  +0.000009]  driver_register+0x1a8/0x3e4
[  +0.000009]  __platform_driver_register+0x6c/0x94
[  +0.000008]  meson_drm_platform_driver_init+0x3c/0x1000 [meson_drm]
[  +0.000027]  do_one_initcall+0xc4/0x2b0
[  +0.000011]  do_init_module+0x154/0x570
[  +0.000011]  load_module+0x1a78/0x1ea4
[  +0.000008]  __do_sys_init_module+0x184/0x1cc
[  +0.000009]  __arm64_sys_init_module+0x78/0xb0
[  +0.000009]  invoke_syscall+0x74/0x260
[  +0.000009]  el0_svc_common.constprop.0+0xcc/0x260
[  +0.000008]  do_el0_svc+0x50/0x70
[  +0.000007]  el0_svc+0x68/0x1a0
[  +0.000012]  el0t_64_sync_handler+0x11c/0x150
[  +0.000008]  el0t_64_sync+0x18c/0x190

[  +0.000016] Allocated by task 879:
[  +0.000008]  kasan_save_stack+0x2c/0x5c
[  +0.000011]  __kasan_kmalloc+0x90/0xd0
[  +0.000007]  __kmalloc+0x278/0x4a0
[  +0.000011]  mpi_resize+0x13c/0x1d0
[  +0.000011]  mpi_powm+0xd24/0x1570
[  +0.000009]  rsa_enc+0x1a4/0x30c
[  +0.000009]  pkcs1pad_verify+0x3f0/0x580
[  +0.000009]  public_key_verify_signature+0x7a8/0xba4
[  +0.000010]  public_key_verify_signature_2+0x40/0x60
[  +0.000008]  verify_signature+0xb4/0x114
[  +0.000008]  pkcs7_validate_trust_one.constprop.0+0x3b8/0x574
[  +0.000009]  pkcs7_validate_trust+0xb8/0x15c
[  +0.000008]  verify_pkcs7_message_sig+0xec/0x1b0
[  +0.000012]  verify_pkcs7_signature+0x78/0xac
[  +0.000007]  mod_verify_sig+0x110/0x190
[  +0.000009]  module_sig_check+0x114/0x1e0
[  +0.000009]  load_module+0xa0/0x1ea4
[  +0.000008]  __do_sys_init_module+0x184/0x1cc
[  +0.000008]  __arm64_sys_init_module+0x78/0xb0
[  +0.000008]  invoke_syscall+0x74/0x260
[  +0.000009]  el0_svc_common.constprop.0+0x1a8/0x260
[  +0.000008]  do_el0_svc+0x50/0x70
[  +0.000007]  el0_svc+0x68/0x1a0
[  +0.000009]  el0t_64_sync_handler+0x11c/0x150
[  +0.000009]  el0t_64
---truncated---


Remediation: