[PATCH v2] drm: Protect drm_connector_register_all() under DRIVER_MODESET

[Emil Velikov]

On 18 June 2016 at 14:46, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> 0-day kbuilder found
>
> [    1.360244] BUG: unable to handle kernel NULL pointer dereference at   (null)
> [    1.360972] IP: [<c14db9ad>] mutex_lock_nested+0x11f/0x2c3
> [    1.361512] *pde = 00000000
> [    1.361827] Oops: 0002 [#1]
> [    1.362123] Modules linked in:
> [    1.362451] CPU: 0 PID: 1 Comm: swapper Not tainted 4.7.0-rc2-00564-ge28cd4d #1
> [    1.363202] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014
> [    1.364105] task: c03d0000 ti: d28da000 task.ti: d28da000
> [    1.364636] EIP: 0060:[<c14db9ad>] EFLAGS: 00210096 CPU: 0
> [    1.365215] EIP is at mutex_lock_nested+0x11f/0x2c3
> [    1.365703] EAX: 00000000 EBX: d39e8ae8 ECX: d39e8b14 EDX: c1361cf9
> [    1.366351] ESI: c03d0000 EDI: d28dbed0 EBP: d28dbeec ESP: d28dbec0
> [    1.367010]  DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068
> [    1.367534] CR0: 80050033 CR2: 00000000 CR3: 019a9000 CR4: 00000690
> [    1.368152] Stack:
> [    1.368356]  d39e8b14 d39e8b24 c1361cf9 00200246 d39e8b14 00000000 11111111 d28dbed0
> [    1.369235]  d39e8800 d39e8ae8 00000000 d28dbf08 c1361cf9 d28dbf0c c10b25be d39e8800
> [    1.370087]  00000000 00000000 d28dbf1c c135e37d fffffff4 ffffffff 00000000 d28dbf28
> [    1.371012] Call Trace:
> [    1.371272]  [<c1361cf9>] ? drm_connector_register_all+0x1a/0x92
> [    1.371847]  [<c1361cf9>] drm_connector_register_all+0x1a/0x92
> [    1.372421]  [<c10b25be>] ? kstrdup+0x25/0x3a
> [    1.372863]  [<c135e37d>] drm_dev_register+0x59/0x99
> [    1.373358]  [<c195ea3e>] vgem_init+0x34/0x49
> [    1.373770]  [<c195ea0a>] ? mipi_dsi_bus_init+0xf/0xf
> [    1.374257]  [<c100048f>] do_one_initcall+0x7c/0xfd
> [    1.374754]  [<c104b409>] ? parse_args+0x1fd/0x314
> [    1.375259]  [<c1939c10>] ? kernel_init_freeable+0xd0/0x179
> [    1.375837]  [<c1939c2c>] kernel_init_freeable+0xec/0x179
> [    1.376371]  [<c14d66ea>] kernel_init+0x8/0xcb
> [    1.376806]  [<c14debce>] ret_from_kernel_thread+0xe/0x30
> [    1.377322]  [<c14d66e2>] ? rest_init+0x10e/0x10e
> [    1.377754] Code: 89 fa e8 71 c5 b7 ff 8b 4e 04 89 fa 89 d8 e8 8e c6 b7 ff 8d 43 2c 89 45 d4 8b 43 30 8d 4b 2c 89 45 e8 89 7b 30 89 4d e4 8b 55 dc <89> 38 8d 43 3c 89 75 ec e8 c9 dd b7 ff eb 0c 31 c0 87 03 48
> +75
> [    1.380442] EIP: [<c14db9ad>] mutex_lock_nested+0x11f/0x2c3 SS:ESP 0068:d28dbec0
> [    1.381174] CR2: 0000000000000000
>
> when loading the non-modesetting vGEM module. To prevent use of the
> uninitialised dev->mode_config from drm_dev_register() we move the
> drm_connector_register_all() under a DRIVER_MODESET guard. Longer term,
> we probably want to initialise the embedded dev->mode_config automatically
> from drm_dev_init() for all DRIVER_MODESET drivers.
>
> v2: Also protect drm_dev_unregister.
>
> Fixes: e28cd4d0a223 ("drm: Automatically register/unregister all connectors")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Emil Velikov <emil.l.velikov at gmail.com>

Reviewed-by: Emil Velikov <emil.l.velikov at gmail.com>

Thanks
Emil