CVE-2021-47119

/// Technical description

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.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References