CVE-2025-21853

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/[email protected]/