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SubjectRe: [PATCH] drm/bridge: megachips: Fix a null pointer dereference bug
On Sat, 16 Jul 2022 at 10:13, Zheyu Ma <zheyuma97@gmail.com> wrote:
>
> When removing the module we will get the following warning:
>
> [ 31.911505] i2c-core: driver [stdp2690-ge-b850v3-fw] unregistered
> [ 31.912484] general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN PTI
> [ 31.913338] KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
> [ 31.915280] RIP: 0010:drm_bridge_remove+0x97/0x130
> [ 31.921825] Call Trace:
> [ 31.922533] stdp4028_ge_b850v3_fw_remove+0x34/0x60 [megachips_stdpxxxx_ge_b850v3_fw]
> [ 31.923139] i2c_device_remove+0x181/0x1f0
>
> The two bridges (stdp2690, stdp4028) do not probe at the same time, so
> the driver does not call ge_b850v3_resgiter() when probing, causing the
> driver to try to remove the object that has not been initialized.
>
> Fix this by checking whether both the bridges are probed.
>
> Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
> ---
> drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> index cce98bf2a4e7..c68a4cdf4625 100644
> --- a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> +++ b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> @@ -296,7 +296,9 @@ static void ge_b850v3_lvds_remove(void)
> * This check is to avoid both the drivers
> * removing the bridge in their remove() function
> */
> - if (!ge_b850v3_lvds_ptr)
> + if (!ge_b850v3_lvds_ptr ||
> + !ge_b850v3_lvds_ptr->stdp2690_i2c ||
> + !ge_b850v3_lvds_ptr->stdp4028_i2c)

This chunk fails checkpatch --strict.

Alignment should match open parenthesis
#39: FILE: drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c:300:


> goto out;
>
> drm_bridge_remove(&ge_b850v3_lvds_ptr->bridge);
> --
> 2.25.1
>

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