Re: [PATCH 1/1] drm/i915: fix race condition UAF in i915_perf_add_config_ioctl

[Tvrtko Ursulin]

On 28/03/2023 10:36, Min Li wrote:
> Userspace can guess the id value and try to race oa_config object creation
> with config remove, resulting in a use-after-free if we dereference the
> object after unlocking the metrics_lock.  For that reason, unlocking the
> metrics_lock must be done after we are done dereferencing the object.
>
> Signed-off-by: Min Li <lm0963hack@xxxxxxxxx>

Fixes: f89823c21224 ("drm/i915/perf: Implement I915_PERF_ADD/REMOVE_CONFIG interface")
Cc: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v4.14+

> ---
>   drivers/gpu/drm/i915/i915_perf.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
> index 824a34ec0b83..93748ca2c5da 100644
> --- a/drivers/gpu/drm/i915/i915_perf.c
> +++ b/drivers/gpu/drm/i915/i915_perf.c
> @@ -4634,13 +4634,13 @@ int i915_perf_add_config_ioctl(struct drm_device *dev, void *data,
>   		err = oa_config->id;
>   		goto sysfs_err;
>   	}
> -
> -	mutex_unlock(&perf->metrics_lock);
> +	id = oa_config->id;
>   
>   	drm_dbg(&perf->i915->drm,
>   		"Added config %s id=%i\n", oa_config->uuid, oa_config->id);
> +	mutex_unlock(&perf->metrics_lock);
>   
> -	return oa_config->id;
> +	return id;
>   
>   sysfs_err:
>   	mutex_unlock(&perf->metrics_lock);

LGTM.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Umesh or Lionel could you please double check? I can merge if confirmed okay.

Regards,

Tvrtko