[PATCH] cifs: prevent updating file size from server if we have a read/write lease

[Bharath SM <bharathsm.hsk@gmail.com>]

In cases of large directories, the readdir operation may span multiple
round trips to retrieve contents. This introduces a potential race
condition in case of concurrent write and readdir operations. If the
readdir operation initiates before a write has been processed by the
server, it may update the file size attribute to an older value.
Address this issue by avoiding file size updates from server when a
read/write lease.

Scenario:
1) process1: open dir xyz
2) process1: readdir instance 1 on xyz
3) process2: create file.txt for write
4) process2: write x bytes to file.txt
5) process2: close file.txt
6) process2: open file.txt for read
7) process1: readdir 2 - overwrites file.txt inode size to 0
8) process2: read contents of file.txt - bug, short read with 0 bytes

Signed-off-by: Bharath SM <bharathsm@microsoft.com>
---
 fs/smb/client/file.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index f2db4a1f81ad..e742d0d0e579 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -2952,7 +2952,8 @@ bool is_size_safe_to_change(struct cifsInodeInfo *cifsInode, __u64 end_of_file)
 	if (!cifsInode)
 		return true;
 
-	if (is_inode_writable(cifsInode)) {
+	if (is_inode_writable(cifsInode) ||
+			((cifsInode->oplock & CIFS_CACHE_RW_FLG) != 0)) {
 		/* This inode is open for write at least once */
 		struct cifs_sb_info *cifs_sb;
 
-- 
2.34.1