linux-kernel - [PATCH v3] cifs: Fix copy_to

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Message-ID: <20251007041209.99174-1-wangfushuai@baidu.com>
Date: Tue, 7 Oct 2025 12:12:09 +0800
From: Fushuai Wang <wangfushuai@...du.com>
To: <sfrench@...ba.org>, <pc@...guebit.org>, <ronniesahlberg@...il.com>,
	<sprasad@...rosoft.com>, <tom@...pey.com>, <bharathsm@...rosoft.com>
CC: <linux-cifs@...r.kernel.org>, <samba-technical@...ts.samba.org>,
	<linux-kernel@...r.kernel.org>, Fushuai Wang <wangfushuai@...du.com>
Subject: [PATCH v3] 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: d08089f649a0 ("cifs: Change the I/O paths to use an iterator rather than a page list")
Signed-off-by: Fushuai Wang <wangfushuai@...du.com>
---
 fs/smb/client/smb2ops.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index 058050f744c0..ac8a5bd6aec4 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -4650,7 +4650,7 @@ 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) {
@@ -4763,10 +4763,10 @@ 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 -1;
+		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");
-- 
2.36.1