cifs: don't update i_size in cifs_do_truncate without a cached handle

If find_writable_file() returns null, cifs_file_flush will return
0 without issuing set_file_size, and the outer 'if (!rc)' block
will set i_size to 0 before telling the server to truncate.  If
the cifs_open() then fails, the inode will have size 0, while
the server file is unchanged.

Move the netfs_resize_file() and cifs_setsize() into the 'if
(cfile)', so they only run after a successful set_file_size.

In the no-handle else branch, evict stale pages with
truncate_inode_pages before the O_TRUNC open to dispose of old
cache pages, and let the open response set the i_size.

Fixes: 110fee6b9bb5 ("smb: client: fix missing timestamp updates with O_TRUNC")
Cc: stable@vger.kernel.org
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>

1 files changed, 20 insertions, 4 deletions

diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index 389083f9ce00..100acc76e9be 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -1012,10 +1012,26 @@ static int cifs_do_truncate(const unsigned int xid, struct dentry *dentry)
 			server = tcon->ses->server;
 			rc = server->ops->set_file_size(xid, tcon,
 							cfile, 0, false);
-		}
-		if (!rc) {
-			netfs_resize_file(&cinode->netfs, 0, true);
-			cifs_setsize(inode, 0);
+			if (!rc) {
+				inode_lock(inode);
+				filemap_invalidate_lock(inode->i_mapping);
+				netfs_resize_file(&cinode->netfs, 0, true);
+				cifs_setsize(inode, 0);
+				filemap_invalidate_unlock(inode->i_mapping);
+				inode_unlock(inode);
+				cifs_invalidate_cache(inode, 0);
+			}
+		} else {
+			/*
+			 * No cached handle; evict stale pages so they can't
+			 * be served after the file is later extended; let
+			 * the server's O_TRUNC open response set the i_size
+			 */
+			inode_lock(inode);
+			filemap_invalidate_lock(inode->i_mapping);
+			truncate_inode_pages(inode->i_mapping, 0);
+			filemap_invalidate_unlock(inode->i_mapping);
+			inode_unlock(inode);
 			cifs_invalidate_cache(inode, 0);
 		}
 	}