CVE-2025-21812

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

ax25: rcu protect dev->ax25_ptr

syzbot found a lockdep issue [1].

We should remove ax25 RTNL dependency in ax25_setsockopt()

This should also fix a variety of possible UAF in ax25.

[1]

WARNING: possible circular locking dependency detected

6.13.0-rc3-syzkaller-00762-g9268abe611b0 #0 Not tainted

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syz.5.1818/12806 is trying to acquire lock:

ffffffff8fcb3988 (rtnl_mutex){+.+.}-{4:4}, at: ax25_setsockopt+0xa55/0xe90 net/ax25/af_ax25.c:680

but task is already holding lock:

ffff8880617ac258 (sk_lock-AF_AX25){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1618 [inline]

ffff8880617ac258 (sk_lock-AF_AX25){+.+.}-{0:0}, at: ax25_setsockopt+0x209/0xe90 net/ax25/af_ax25.c:574

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (sk_lock-AF_AX25){+.+.}-{0:0}:

lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:58

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References