CVE-2021-47119 ext4: fix memory leak in ext4_fill_super
A memory leak in the Linux kernel ext4 filesystem allows attackers to cause denial of service by repeatedly mounting and unmounting volumes.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-47119?
CVE-2021-47119 is a medium-severity denial of service vulnerability in Linux kernel, published on 15 Mar 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-401
Which versions are affected by CVE-2021-47119?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2021-47119?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2021-47119 being exploited?
There is no known exploitation of CVE-2021-47119 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2021-47119, GHSA-xv6r-2m8v-f893, UBUNTU-CVE-2021-47119.