ext2: fix potential use after free

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>

diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
index 62d9a659a8ff4e7a3a9556449e35fecc25612e43..dd8f10db82e992da8b8f4fb37699d7bf4a87cf4d 100644 (file)
--- a/fs/ext2/xattr.c
+++ b/fs/ext2/xattr.c
@@ -612,9 +612,9 @@ bad_block:          ext2_error(sb, "ext2_xattr_set",
        }
 
 cleanup:
-       brelse(bh);
        if (!(bh && header == HDR(bh)))
                kfree(header);
+       brelse(bh);
        up_write(&EXT2_I(inode)->xattr_sem);
 
        return error;