cifs: Fix copy_to_iter return value check

The return value of copy_to_iter() function will never be negative,
it is the number of bytes copied, or zero if nothing was copied.
Update the check to treat 0 as an error, and return -1 in that case.

Fixes: d08089f ("cifs: Change the I/O paths to use an iterator rather than a page list")
Acked-by: Tom Talpey <[email protected]>
Reviewed-by: David Howells <[email protected]>
Signed-off-by: Fushuai Wang <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: Fushuai Wang

fs/smb/client/smb2ops.c

@@ -4736,7 +4736,7 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
 	unsigned int pad_len;
 	struct cifs_io_subrequest *rdata = mid->callback_data;
 	struct smb2_hdr *shdr = (struct smb2_hdr *)buf;
-	int length;
+	size_t copied;
 	bool use_rdma_mr = false;
 
 	if (shdr->Command != SMB2_READ) {
@@ -4849,10 +4849,10 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
 	} else if (buf_len >= data_offset + data_len) {
 		/* read response payload is in buf */
 		WARN_ONCE(buffer, "read data can be either in buf or in buffer");
-		length = copy_to_iter(buf + data_offset, data_len, &rdata->subreq.io_iter);
-		if (length < 0)
-			return length;
-		rdata->got_bytes = data_len;
+		copied = copy_to_iter(buf + data_offset, data_len, &rdata->subreq.io_iter);
+		if (copied == 0)
+			return -EIO;
+		rdata->got_bytes = copied;
 	} else {
 		/* read response payload cannot be in both buf and pages */
 		WARN_ONCE(1, "buf can not contain only a part of read data");