[PATCH] fs: Fix truncate never updates m/ctime

[Jubin Zhong]

From: zhongjubin <zhongjubin@xxxxxxxxxx>

Syscall truncate() never updates m/ctime even if the file size is
changed. However, this is incorrect according to man file:

  truncate (2):
  If  the  size  changed, then the st_ctime and st_mtime fields
  (respectively, time of last status change and time of last modification;
  see stat(2)) for the file are updated, and the set-user-ID and
  set-group-ID mode bits may be cleared.

Check file size before do_truncate() to fix this.

Signed-off-by: zhongjubin <zhongjubin@xxxxxxxxxx>
---
 fs/open.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index f732fb94600c..02404b759c2e 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -106,8 +106,11 @@ long vfs_truncate(const struct path *path, loff_t length)
 		goto put_write_and_out;
 
 	error = security_path_truncate(path);
-	if (!error)
-		error = do_truncate(mnt_userns, path->dentry, length, 0, NULL);
+	if (error)
+		goto put_write_and_out;
+
+	if (i_size_read(inode) != length)
+		error = do_truncate(mnt_userns, path->dentry, length, ATTR_MTIME | ATTR_CTIME, NULL);
 
 put_write_and_out:
 	put_write_access(inode);
-- 
2.12.3