CVE-2025-21853 Information

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/

Reference

https://git.kernel.org/stable/c/271e49f8a58edba65bc2b1250a0abaa98c4bfdbe https://git.kernel.org/stable/c/29cfda62ab4d92ab94123813db49ab76c1e61b29 https://git.kernel.org/stable/c/bc27c52eea189e8f7492d40739b7746d67b65beb https://git.kernel.org/stable/c/d95607a5f2f9bb08194c9deaf4a5f3e8ba59a9d4