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

[Umesh Nerlige Ramappa]

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 <lm0963h...@gmail.com>

Fixes: f89823c21224 ("drm/i915/perf: Implement I915_PERF_ADD/REMOVE_CONFIG 
interface")
Cc: Lionel Landwerlin <lionel.g.landwer...@intel.com>
Cc: Umesh Nerlige Ramappa <umesh.nerlige.rama...@intel.com>
Cc: <sta...@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.ursu...@intel.com>

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

LGTM,

Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.rama...@intel.com>

Thanks,
Umesh

Regards,

Tvrtko