drm/xe/oa: Fix potential UAF in xe_oa_add_config_ioctl()

In xe_oa_add_config_ioctl(), we accessed oa_config->id after dropping
metrics_lock. Since this lock protects the lifetime of oa_config, an
attacker could guess the id and call xe_oa_remove_config_ioctl() with
perfect timing, freeing oa_config before we dereference it, leading to
a potential use-after-free.

Fix this by caching the id in a local variable while holding the lock.

v2: (Matt A)
- Dropped mutex_unlock(&oa->metrics_lock) ordering change from
  xe_oa_remove_config_ioctl()

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/6614
Fixes: cdf02fe ("drm/xe/oa/uapi: Add/remove OA config perf ops")
Cc: <stable@vger.kernel.org> # v6.11+
Suggested-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patch.msgid.link/20251118114859.3379952-2-sanjay.kumar.yadav@intel.com
(cherry picked from commit 28aeaed)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Author: sanjayumang

drivers/gpu/drm/xe/xe_oa.c

@@ -2403,11 +2403,13 @@ int xe_oa_add_config_ioctl(struct drm_device *dev, u64 data, struct drm_file *fi
 		goto sysfs_err;
 	}
 
-	mutex_unlock(&oa->metrics_lock);
+	id = oa_config->id;
+
+	drm_dbg(&oa->xe->drm, "Added config %s id=%i\n", oa_config->uuid, id);
 
-	drm_dbg(&oa->xe->drm, "Added config %s id=%i\n", oa_config->uuid, oa_config->id);
+	mutex_unlock(&oa->metrics_lock);
 
-	return oa_config->id;
+	return id;
 
 sysfs_err:
 	mutex_unlock(&oa->metrics_lock);