CVE-2025-21853: bpf: avoid holding freeze_mutex during mmap operation

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-03-12 · updated 2026-10-15

Description

In the Linux kernel, the following vulnerability has been resolved: bpf: avoid holding freeze_mutex during mmap operation We use map->freeze_mutex to prevent races between map_freeze() and memory mapping BPF map contents with writable permissions. The way we naively do this means we'll hold freeze_mutex for entire duration of all the mm and VMA manipulations, which is completely unnecessary. This can potentially also lead to deadlocks, as reported by syzbot in [0]. So, instead, hold freeze_mutex only during writeability checks, bump (proactively) "write active" count for the map, unlock the mutex and proceed with mmap logic. And only if something went wrong during mmap logic, then undo that "write active" counter increment. [0] https://lore.kernel.org/bpf/678dcbc9.050a0220.303755.0066.GAE@google.com/

Affected products

Linux kernel: from 5.5 before 6.6.80; from 6.7 before 6.12.17; from 6.13 before 6.13.5; 6.14-rc1, 6.14-rc2, 6.14-rc3 — fixed in 6.12.17, 6.13.5, 6.6.80

How to fix

Upgrade to a fixed version: Linux kernel 6.12.17, 6.13.5, 6.6.80. Check the vendor advisory for mitigations.

References

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