CVE-2021-47119: ext4: fix memory leak in ext4_fill_super

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-03-15 · updated 2026-06-17
Weakness: CWE-401

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.

Affected products

Linux kernel: from 2.6.19 before 5.10.43; from 5.11 before 5.12.10; 5.13-rc1, 5.13-rc2, 5.13-rc3, 5.13-rc4 — fixed in 5.10.43, 5.12.10

How to fix

Upgrade to a fixed version: Linux kernel 5.10.43, 5.12.10. Check the vendor advisory for mitigations.

References

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