[PATCH] drm/ast: Allocate initial CRTC state of the correct size

[Konstantin Khlebnikov]

On 20/04/2020 15.55, Thomas Zimmermann wrote:
> Hi Konstantin
> 
> Am 20.04.20 um 14:45 schrieb Konstantin Khlebnikov:
>> I've stumbled upon this too. Trivial fix was posted but stuck in review.
>> This is patch from Thomas Zimmermann changed according to suggestions by
>> Daniel Vetter from https://patchwork.kernel.org/patch/11356157/
> 
> Did you find it on the mailing list? I was waiting for this patch to get
> merged. Apparently I forgot to push it? I'll take care of the patch.

Ah, my bad. After deeper look I've found v2
https://patchwork.kernel.org/patch/11357645/
But in State=New, it's definitely lost

> 
> Best regards
> Thomas
> 
>>
>>
>> The ast driver inherits from DRM's CRTC state, but still uses the atomic
>> helper for struct drm_crtc_funcs.reset, drm_atomic_helper_crtc_reset().
>>
>> The helper only allocates enough memory for the core CRTC state. That
>> results in an out-ouf-bounds access when duplicating the initial CRTC
>> state. Simplified backtrace shown below:
>>
>> [   21.469321] ==================================================================
>> [   21.469434] BUG: KASAN: slab-out-of-bounds in ast_crtc_atomic_duplicate_state+0x84/0x100 [ast]
>> [   21.469445] Read of size 8 at addr ffff888036c1c5f8 by task systemd-udevd/382
>> [   21.469451]
>> [   21.469464] CPU: 2 PID: 382 Comm: systemd-udevd Tainted: G            E     5.5.0-rc6-1-default+ #214
>> [   21.469473] Hardware name: Sun Microsystems SUN FIRE X2270 M2/SUN FIRE X2270 M2, BIOS 2.05    07/01/2010
>> [   21.469480] Call Trace:
>> [   21.469501]  dump_stack+0xb8/0x110
>> [   21.469528]  print_address_description.constprop.0+0x1b/0x1e0
>> [   21.469557]  ? ast_crtc_atomic_duplicate_state+0x84/0x100 [ast]
>> [   21.469581]  ? ast_crtc_atomic_duplicate_state+0x84/0x100 [ast]
>> [   21.469597]  __kasan_report.cold+0x1a/0x35
>> [   21.469640]  ? ast_crtc_atomic_duplicate_state+0x84/0x100 [ast]
>> [   21.469665]  kasan_report+0xe/0x20
>> [   21.469693]  ast_crtc_atomic_duplicate_state+0x84/0x100 [ast]
>> [   21.469733]  drm_atomic_get_crtc_state+0xbf/0x1c0
>> [   21.469768]  __drm_atomic_helper_set_config+0x81/0x5a0
>> [   21.469803]  ? drm_atomic_plane_check+0x690/0x690
>> [   21.469843]  ? drm_client_rotation+0xae/0x240
>> [   21.469876]  drm_client_modeset_commit_atomic+0x230/0x390
>> [   21.469888]  ? __mutex_lock+0x8f0/0xbe0
>> [   21.469929]  ? drm_client_firmware_config.isra.0+0xa60/0xa60
>> [   21.469948]  ? drm_client_modeset_commit_force+0x28/0x230
>> [   21.470031]  ? memset+0x20/0x40
>> [   21.470078]  drm_client_modeset_commit_force+0x90/0x230
>> [   21.470110]  drm_fb_helper_restore_fbdev_mode_unlocked+0x5f/0xc0
>> [   21.470132]  drm_fb_helper_set_par+0x59/0x70
>> [   21.470155]  fbcon_init+0x61d/0xad0
>> [   21.470185]  ? drm_fb_helper_restore_fbdev_mode_unlocked+0xc0/0xc0
>> [   21.470232]  visual_init+0x187/0x240
>> [   21.470266]  do_bind_con_driver+0x2e3/0x460
>> [   21.470321]  do_take_over_console+0x20a/0x290
>> [   21.470371]  do_fbcon_takeover+0x85/0x100
>> [   21.470402]  register_framebuffer+0x2fd/0x490
>> [   21.470425]  ? kzalloc.constprop.0+0x10/0x10
>> [   21.470503]  __drm_fb_helper_initial_config_and_unlock+0xf2/0x140
>> [   21.470533]  drm_fbdev_client_hotplug+0x162/0x250
>> [   21.470563]  drm_fbdev_generic_setup+0xd2/0x155
>> [   21.470602]  ast_driver_load+0x688/0x850 [ast]
>> <...>
>> [   21.472625] ==================================================================
>>
>> Allocating enough memory for struct ast_crtc_state in a custom ast CRTC
>> reset handler fixes the problem.
>>
>> Signed-off-by: Konstantin Khlebnikov <khlebnikov at yandex-team.ru>
>> Fixes: 83be6a3ceb11 ("drm/ast: Introduce struct ast_crtc_state")
>> Link: https://patchwork.kernel.org/patch/11356157/
>> Cc: Thomas Zimmermann <tzimmermann at suse.de>
>> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>> ---
>>   drivers/gpu/drm/ast/ast_mode.c |   13 ++++++++++++-
>>   1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
>> index cdd6c46d6557..17143e6bbfec 100644
>> --- a/drivers/gpu/drm/ast/ast_mode.c
>> +++ b/drivers/gpu/drm/ast/ast_mode.c
>> @@ -918,8 +918,19 @@ static void ast_crtc_atomic_destroy_state(struct drm_crtc *crtc,
>>   	kfree(ast_state);
>>   }
>>   
>> +static void ast_crtc_reset(struct drm_crtc *crtc)
>> +{
>> +	struct ast_crtc_state *state =
>> +		kzalloc(sizeof(*state), GFP_KERNEL);
>> +
>> +	if (crtc->state)
>> +		ast_crtc_atomic_destroy_state(crtc, crtc->state);
>> +
>> +	__drm_atomic_helper_crtc_reset(crtc, &state->base);
>> +}
>> +
>>   static const struct drm_crtc_funcs ast_crtc_funcs = {
>> -	.reset = drm_atomic_helper_crtc_reset,
>> +	.reset = ast_crtc_reset,
>>   	.set_config = drm_crtc_helper_set_config,
>>   	.gamma_set = drm_atomic_helper_legacy_gamma_set,
>>   	.destroy = ast_crtc_destroy,
>>
>