[PATCH 6.8 687/715] ceph: stop copying to iter at EOF on sync reads

[Sasha Levin]

From: Xiubo Li <xiubli@xxxxxxxxxx>

[ Upstream commit 1065da21e5df9d843d2c5165d5d576be000142a6 ]

If EOF is encountered, ceph_sync_read() return value is adjusted down
according to i_size, but the "to" iter is advanced by the actual number
of bytes read.  Then, when retrying, the remainder of the range may be
skipped incorrectly.

Ensure that the "to" iter is advanced only until EOF.

[ idryomov: changelog ]

Fixes: c3d8e0b5de48 ("ceph: return the real size read when it hits EOF")
Reported-by: Frank Hsiao <frankhsiao@xxxxxxxx>
Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
Reviewed-by: Ilya Dryomov <idryomov@xxxxxxxxx>
Tested-by: Frank Hsiao <frankhsiao@xxxxxxxx>
Signed-off-by: Ilya Dryomov <idryomov@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/ceph/file.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index abe8028d95bf4..3d1cd079dbf16 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -1138,7 +1138,12 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos,
 		}
 
 		idx = 0;
-		left = ret > 0 ? ret : 0;
+		if (ret <= 0)
+			left = 0;
+		else if (off + ret > i_size)
+			left = i_size - off;
+		else
+			left = ret;
 		while (left > 0) {
 			size_t plen, copied;
 
@@ -1167,15 +1172,13 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos,
 	}
 
 	if (ret > 0) {
-		if (off > *ki_pos) {
-			if (off >= i_size) {
-				*retry_op = CHECK_EOF;
-				ret = i_size - *ki_pos;
-				*ki_pos = i_size;
-			} else {
-				ret = off - *ki_pos;
-				*ki_pos = off;
-			}
+		if (off >= i_size) {
+			*retry_op = CHECK_EOF;
+			ret = i_size - *ki_pos;
+			*ki_pos = i_size;
+		} else {
+			ret = off - *ki_pos;
+			*ki_pos = off;
 		}
 
 		if (last_objver)
-- 
2.43.0