smb: avoid pointless cred reference count bump

The creds are allocated via prepare_kernel_cred() which has already
taken a reference.

This also removes a pointless check that gives the impression that
override_creds() can ever be called on a task with current->cred NULL.
That's not possible afaict. Remove the check to not imply that there can
be a dangling pointer in current->cred.

Link: https://lore.kernel.org/r/20241125-work-cred-v2-21-68b9d38bb5b2@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

fs/smb/server/smb_common.c

@@ -780,11 +780,7 @@ int __ksmbd_override_fsids(struct ksmbd_work *work,
 		cred->cap_effective = cap_drop_fs_set(cred->cap_effective);
 
 	WARN_ON(work->saved_cred);
-	work->saved_cred = override_creds(get_new_cred(cred));
-	if (!work->saved_cred) {
-		abort_creds(cred);
-		return -EINVAL;
-	}
+	work->saved_cred = override_creds(cred);
 	return 0;
 }
 
@@ -796,13 +792,11 @@ int ksmbd_override_fsids(struct ksmbd_work *work)
 void ksmbd_revert_fsids(struct ksmbd_work *work)
 {
 	const struct cred *cred;
-
 	WARN_ON(!work->saved_cred);
 
-	cred = current_cred();
-	put_cred(revert_creds(work->saved_cred));
-	put_cred(cred);
+	cred = revert_creds(work->saved_cred);
 	work->saved_cred = NULL;
+	put_cred(cred);
 }
 
 __le32 smb_map_generic_desired_access(__le32 daccess)