ext4: fix kernel infoleak via ext4_extent_header

stable inclusion
from linux-4.19.198
commit 9ed3a3d3a8d2cbe99d9e4386a98856491f0eade0

--------------------------------

commit ce3aba43 upstream.

Initialize eh_generation of struct ext4_extent_header to prevent leaking
info to userspace. Fixes KMSAN kernel-infoleak bug reported by syzbot at:
http://syzkaller.appspot.com/bug?id=78e9ad0e6952a3ca16e8234724b2fa92d041b9b8



Cc: stable@kernel.org
Reported-by:  <syzbot+2dcfeaf8cb49b05e8f1a@syzkaller.appspotmail.com>
Fixes: a86c6181 ("[PATCH] ext3: add extent map support")
Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
Link: https://lore.kernel.org/r/20210506185655.7118-1-mail@anirudhrb.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>