nfsd: call op_release, even when op_func returns an error

For ops with "trivial" replies, nfsd4_encode_operation will shortcut
most of the encoding work and skip to just marshalling up the status.
One of the things it skips is calling op_release. This could cause a
memory leak in the layoutget codepath if there is an error at an
inopportune time.

Have the compound processing engine always call op_release, even when
op_func sets an error in op->status. With this change, we also need
nfsd4_block_get_device_info_scsi to set the gd_device pointer to NULL
on error to avoid a double free.
Reported-by: Zhi Li <yieli@redhat.com>
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2181403
Fixes: 34b1744c ("nfsd4: define ->op_release for compound ops")
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/blocklayout.c

@@ -297,6 +297,7 @@ nfsd4_block_get_device_info_scsi(struct super_block *sb,
 
 out_free_dev:
 	kfree(dev);
+	gdp->gd_device = NULL;
 	return ret;
 }
 

fs/nfsd/nfs4xdr.c

@@ -5400,10 +5400,8 @@ nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
 	__be32 *p;
 
 	p = xdr_reserve_space(xdr, 8);
-	if (!p) {
-		WARN_ON_ONCE(1);
-		return;
-	}
+	if (!p)
+		goto release;
 	*p++ = cpu_to_be32(op->opnum);
 	post_err_offset = xdr->buf->len;
 
@@ -5418,8 +5416,6 @@ nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
 	op->status = encoder(resp, op->status, &op->u);
 	if (op->status)
 		trace_nfsd_compound_encode_err(rqstp, op->opnum, op->status);
-	if (opdesc && opdesc->op_release)
-		opdesc->op_release(&op->u);
 	xdr_commit_encode(xdr);
 
 	/* nfsd4_check_resp_size guarantees enough room for error status */
@@ -5460,6 +5456,9 @@ nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
 	}
 status:
 	*p = op->status;
+release:
+	if (opdesc && opdesc->op_release)
+		opdesc->op_release(&op->u);
 }
 
 /*