erofs: use credential guards

Use credential guards for scoped credential override with automatic
restoration on scope exit.

Link: https://patch.msgid.link/20251103-work-creds-guards-simple-v1-9-a3e156839e7f@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

fs/erofs/fileio.c

@@ -47,7 +47,6 @@ static void erofs_fileio_ki_complete(struct kiocb *iocb, long ret)
 
 static void erofs_fileio_rq_submit(struct erofs_fileio_rq *rq)
 {
-	const struct cred *old_cred;
 	struct iov_iter iter;
 	int ret;
 
@@ -61,9 +60,8 @@ static void erofs_fileio_rq_submit(struct erofs_fileio_rq *rq)
 		rq->iocb.ki_flags = IOCB_DIRECT;
 	iov_iter_bvec(&iter, ITER_DEST, rq->bvecs, rq->bio.bi_vcnt,
 		      rq->bio.bi_iter.bi_size);
-	old_cred = override_creds(rq->iocb.ki_filp->f_cred);
-	ret = vfs_iocb_iter_read(rq->iocb.ki_filp, &rq->iocb, &iter);
-	revert_creds(old_cred);
+	scoped_with_creds(rq->iocb.ki_filp->f_cred)
+		ret = vfs_iocb_iter_read(rq->iocb.ki_filp, &rq->iocb, &iter);
 	if (ret != -EIOCBQUEUED)
 		erofs_fileio_ki_complete(&rq->iocb, ret);
 }