[PATCH] cifs: call pagecache_isize_extended() in cifs_setsize() when extending

[Frank Sorenson <sorenson@redhat.com>]

cifs_setsize() calls truncate_pagecache() but skips
pagecache_isize_extended() on extension.  truncate_setsize() shows
the correct pattern:

  i_size_write(inode, newsize);
  if (newsize > oldsize)
      pagecache_isize_extended(inode, oldsize, newsize);
  truncate_pagecache(inode, newsize);

pagecache_isize_extended() zeroes the tail of the page straddling old
EOF.  Without it, dirty bytes in that region can be written back to
the server, exposing stale data in the newly extended range.

Cc: stable@vger.kernel.org
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
---
 fs/smb/client/inode.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/smb/client/inode.c b/fs/smb/client/inode.c
index d459b6f602ca..a5aa1ae23c5f 100644
--- a/fs/smb/client/inode.c
+++ b/fs/smb/client/inode.c
@@ -3059,6 +3059,8 @@ void cifs_setsize(struct inode *inode, loff_t offset)
 		inode->i_blocks = blocks;
 	spin_unlock(&inode->i_lock);
 	inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
+	if (offset > old_size)
+		pagecache_isize_extended(inode, old_size, offset);
 	truncate_pagecache(inode, offset);
 	netfs_wait_for_outstanding_io(inode);
 }
-- 
2.55.0