On Wed, 20 May 2020 at 15:24, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
>
> Some users want to pass NULL to drm_gem_object_put(), but those using
> __drm_gem_object_put() did not. Compromise, have both and let the
> compiler sort it out.
>
> drm_gem_fb_destroy() calls drm_gem_object_put() with NULL obj causing:
> [ 11.584209] BUG: kernel NULL pointer dereference, address: 0000000000000000
> [ 11.584213] #PF: supervisor write access in kernel mode
> [ 11.584215] #PF: error_code(0x0002) - not-present page
> [ 11.584216] PGD 0 P4D 0
> [ 11.584220] Oops: 0002 [#1] SMP NOPTI
> [ 11.584223] CPU: 7 PID: 1571 Comm: gnome-shell Tainted: G E 5.7.0-rc1-1-default+ #27
> [ 11.584225] Hardware name: Micro-Star International Co., Ltd. MS-7A31/X370 XPOWER GAMING TITANIUM (MS-7A31), BIOS 1.MR 12/03/2019
> [ 11.584237] RIP: 0010:drm_gem_fb_destroy+0x28/0x70 [drm_kms_helper]
> <snip>
> [ 11.584256] Call Trace:
> [ 11.584279] drm_mode_rmfb+0x189/0x1c0 [drm]
> [ 11.584299] ? drm_mode_rmfb+0x1c0/0x1c0 [drm]
> [ 11.584314] drm_ioctl_kernel+0xaa/0xf0 [drm]
> [ 11.584329] drm_ioctl+0x1ff/0x3b0 [drm]
> [ 11.584347] ? drm_mode_rmfb+0x1c0/0x1c0 [drm]
> [ 11.584421] amdgpu_drm_ioctl+0x49/0x80 [amdgpu]
> [ 11.584427] ksys_ioctl+0x87/0xc0
> [ 11.584430] __x64_sys_ioctl+0x16/0x20
> [ 11.584434] do_syscall_64+0x5f/0x240
> [ 11.584438] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [ 11.584440] RIP: 0033:0x7f0ef80f7227
>
> Reported-by: Nirmoy Das <nirmoy.das@xxxxxxx>
> Fixes: b5d250744ccc ("drm/gem: fold drm_gem_object_put_unlocked and __drm_gem_object_put()")
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Nirmoy Das <nirmoy.das@xxxxxxx>
> Cc: Emil Velikov <emil.velikov@xxxxxxxxxxxxx>
> Cc: Christian König <christian.koenig@xxxxxxx>.
> Acked-by: Nirmoy Das <nirmoy.das@xxxxxxx>
Reviewed-by: Emil Velikov <emil.velikov@xxxxxxxxxxxxx>
I'm half way through checking the callers and I've noticed a handful of bugs.
Will send the series in due time, although your patch is a perfect
intermediate solution.
Thank you
Emil
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