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

[Tvrtko Ursulin]

On 29/03/2023 01:48, Umesh Nerlige Ramappa wrote:
> On Tue, Mar 28, 2023 at 02:08:47PM +0100, Tvrtko Ursulin wrote:
>>
>> 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 at gmail.com>
>>
>> Fixes: f89823c21224 ("drm/i915/perf: Implement 
>> I915_PERF_ADD/REMOVE_CONFIG interface")
>> Cc: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
>> Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
>> Cc: <stable at vger.kernel.org> # 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 at intel.com>
>>
>> Umesh or Lionel could you please double check? I can merge if 
>> confirmed okay.
> 
> LGTM,
> 
> Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>

Pushed to drm-intel-gt-next, thanks for the fix and reviews!

Regards,

Tvrtko