[PATCH 4/4] ksmbd: enforce write-through on CA share opens

[Yunseong Kim <yunseong.kim@est.tech>]

Per MS-SMB2 3.3.5.9, opens on Continuously Available shares MUST have
FILE_WRITE_THROUGH semantics to ensure data is committed to stable
storage before the operation completes. This is required because
persistent handles may need to be recovered after a server failure, and
any data not flushed to disk would be lost.

Force FILE_WRITE_THROUGH_LE in the CreateOptions passed to
ksmbd_vfs_set_fadvise() for files opened on CA shares, which sets
O_SYNC on the underlying file descriptor.

Signed-off-by: Yunseong Kim <yunseong.kim@est.tech>
---
 fs/smb/server/smb2pdu.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 36efc3f0bf15..beb5120013ed 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -4681,7 +4681,14 @@ int smb2_open(struct ksmbd_work *work)
 		file_info = FILE_CREATED;
 	}
 
-	ksmbd_vfs_set_fadvise(filp, req->CreateOptions);
+	/*
+	 * MS-SMB2 3.3.5.9: Opens on CA shares MUST have FILE_WRITE_THROUGH
+	 * semantics to ensure data is committed to stable storage.
+	 */
+	if (test_share_config_flag(share, KSMBD_SHARE_FLAG_CONTINUOUS_AVAILABILITY))
+		ksmbd_vfs_set_fadvise(filp, req->CreateOptions | FILE_WRITE_THROUGH_LE);
+	else
+		ksmbd_vfs_set_fadvise(filp, req->CreateOptions);
 
 	/* Obtain Volatile-ID */
 	fp = ksmbd_open_fd(work, filp);

-- 
2.47.3