Re: [PATCH] drm/panthor: Fix memory leak in panthor_ioctl_group_create()

[Boris Brezillon <boris.brezillon@collabora.com>]

On Wed, 13 Nov 2024 22:03:39 +0100
Jann Horn <jannh@google.com> wrote:

> When bailing out due to group_priority_permit() failure, the queue_args
> need to be freed. Fix it by rearranging the function to use the
> goto-on-error pattern, such that the success case flows straight without
> indentation while error cases jump forward to cleanup.
> 
> Cc: stable@vger.kernel.org
> Fixes: 5f7762042f8a ("drm/panthor: Restrict high priorities on group_create")
> Signed-off-by: Jann Horn <jannh@google.com>

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> ---
> testcase:
> ```
> #include <err.h>
> #include <fcntl.h>
> #include <stddef.h>
> #include <sys/ioctl.h>
> #include <drm/panthor_drm.h>
> 
> #define SYSCHK(x) ({          \
>   typeof(x) __res = (x);      \
>   if (__res == (typeof(x))-1) \
>     err(1, "SYSCHK(" #x ")"); \
>   __res;                      \
> })
> 
> #define GPU_PATH "/dev/dri/by-path/platform-fb000000.gpu-card"
> 
> int main(void) {
>   int fd = SYSCHK(open(GPU_PATH, O_RDWR));
> 
>   while (1) {
>     struct drm_panthor_queue_create qc[16] = {};
>     struct drm_panthor_group_create gc = {
>       .queues = {
>         .stride = sizeof(struct drm_panthor_queue_create),
>         .count = 16,
>         .array = (unsigned long)qc
>       },
>       .priority = PANTHOR_GROUP_PRIORITY_HIGH+1/*invalid*/
>     };
>     ioctl(fd, DRM_IOCTL_PANTHOR_GROUP_CREATE, &gc);
>   }
> }
> ```
> 
> I have tested that without this patch, after running the testcase for a
> few seconds and then manually killing it, 2G of RAM in kmalloc-128 have
> been leaked. With the patch applied, the memory leak is gone.
> 
> (By the way, get_maintainer.pl suggests that I also send this patch to
> the general DRM maintainers and the DRM-misc maintainers; looking at
> MAINTAINERS, it looks like it is normal that the general DRM maintainers
> are listed for everything under drivers/gpu/, but DRM-misc has exclusion
> rules for a bunch of drivers but not panthor. I don't know if that is
> intentional.)
> ---
>  drivers/gpu/drm/panthor/panthor_drv.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index c520f156e2d73f7e735f8bf2d6d8e8efacec9362..815c23cff25f305d884e8e3e263fa22888f7d5ce 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -1032,14 +1032,15 @@ static int panthor_ioctl_group_create(struct drm_device *ddev, void *data,
>  
>  	ret = group_priority_permit(file, args->priority);
>  	if (ret)
> -		return ret;
> +		goto out;
>  
>  	ret = panthor_group_create(pfile, args, queue_args);
> -	if (ret >= 0) {
> -		args->group_handle = ret;
> -		ret = 0;
> -	}
> +	if (ret < 0)
> +		goto out;
> +	args->group_handle = ret;
> +	ret = 0;
>  
> +out:
>  	kvfree(queue_args);
>  	return ret;
>  }
> 
> ---
> base-commit: 9f8e716d46c68112484a23d1742d9ec725e082fc
> change-id: 20241113-panthor-fix-gcq-bailout-2d9ac36590ed
>