CVE-2021-47119

In the Linux kernel, the following vulnerability has been resolved: ext4:
fix memory leak in ext4_fill_super Buffer head references must be released
before calling kill_bdev(); otherwise the buffer head (and its page
referenced by b_data) will not be freed by kill_bdev, and subsequently that
bh will be leaked. If blocksizes differ, sb_set_blocksize() will kill
current buffers and page cache by using kill_bdev(). And then super block
will be reread again but using correct blocksize this time.
sb_set_blocksize() didn’t fully free superblock page and buffer head, and
being busy, they were not freed and instead leaked. This can easily be
reproduced by calling an infinite loop of: systemctl start
<ext4_on_lvm>.mount, and systemctl stop <ext4_on_lvm>.mount … since
systemd creates a cgroup for each slice which it mounts, and the bh leak
get amplified by a dying memory cgroup that also never gets freed, and
memory consumption is much more easily noticed.