CVE-2025-21879 btrfs: fix use-after-free on inode when scanning root during em shrinking

What is CVE-2025-21879?

CVE-2025-21879 is a high-severity use after free vulnerability in Linux kernel, published on 27 Mar 2025. 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:

btrfs: fix use-after-free on inode when scanning root during em shrinking

At btrfs_scan_root() we are accessing the inode's root (and fs_info) in a call to btrfs_fs_closing() after we have scheduled the inode for a delayed iput, and that can result in a use-after-free on the inode in case the cleaner kthread does the iput before we dereference the inode in the call to btrfs_fs_closing().

Fix this by using the fs_info stored already in a local variable instead of doing inode->root->fs_info.

Weakness: CWE-416

Which versions are affected by CVE-2025-21879?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2025-21879?

Apply the vendor's patch.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2025-21879 being exploited?

There is no known exploitation of CVE-2025-21879 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2025-21879, GHSA-pwxf-vp8f-f327, UBUNTU-CVE-2025-21879.