drm/i915: fix race condition UAF in i915_perf_add_config_ioctl

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@gmail.com>
Fixes: f89823c21224 ("drm/i915/perf: Implement I915_PERF_ADD/REMOVE_CONFIG interface")
Cc: <stable@vger.kernel.org> # v4.14+
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230328093627.5067-1-lm0963hack@gmail.com
[tursulin: Manually added stable tag.]

diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index c035dbb..050b8ae 100644 (file)
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -4802,13 +4802,13 @@ 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);