[PATCH 4.9 32/50] ext2: fix potential use after free

Greg Kroah-Hartman
2018-12-04T11:08:44Z

From: Pan Bian <bianpan2016@163.com>

commit ecebf55d27a11538ea84aee0be643dd953f830d5 upstream.

The function ext2_xattr_set calls brelse(bh) to drop the reference count
of bh. After that, bh may be freed. However, following brelse(bh),
it reads bh->b_data via macro HDR(bh). This may result in a
use-after-free bug. This patch moves brelse(bh) after reading field.

CC: stable@vger.kernel.org
Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ext2/xattr.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/ext2/xattr.c
+++ b/fs/ext2/xattr.c
@@ -609,9 +609,9 @@ skip_replace:
}

cleanup:
- brelse(bh);
if (!(bh && header == HDR(bh)))
kfree(header);
+ brelse(bh);
up_write(&EXT2_I(inode)->xattr_sem);

return error;