[PATCH 5.15.y] ksmbd: return end of file for reads past a named stream's data

[Sasha Levin <sashal@kernel.org>]

From: DaeMyung Kang <charsyam@gmail.com>

[ Upstream commit 626611dc22a3b63b3264a7a797d9dbc530234fcd ]

A READ on a non-empty named stream at or beyond its end fails with
STATUS_INVALID_PARAMETER. ksmbd_vfs_stream_read() returns -EINVAL when
the offset is not below the stream length, and smb2_read() maps -EINVAL
to that status.

smb2_read() already turns a zero-byte read into STATUS_END_OF_FILE, the
status a regular file returns at its end, and an empty stream already
takes that path. Return 0 instead of -EINVAL so that non-empty streams
do the same. Clients that read a stream until end of file otherwise get
an error once they have read all of its data.

The buffered copychunk path converts a zero-byte source read to -EIO,
as it does for a regular file that shrinks during copying.

Fixes: 2ae1a6cc4302 ("cifsd: fix potential read overflow in ksmbd_vfs_stream_read()")
Cc: stable@vger.kernel.org
Signed-off-by: DaeMyung Kang <charsyam@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/ksmbd/vfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ksmbd/vfs.c b/fs/ksmbd/vfs.c
index aff2d0f22c8fb..d27d64ef25528 100644
--- a/fs/ksmbd/vfs.c
+++ b/fs/ksmbd/vfs.c
@@ -299,7 +299,7 @@ static int ksmbd_vfs_stream_read(struct ksmbd_file *fp, char *buf, loff_t *pos,
 		return (int)v_len;
 
 	if (v_len <= *pos) {
-		count = -EINVAL;
+		count = 0;
 		goto free_buf;
 	}
 
-- 
2.53.0