net/packet: avoid fanout hook re-registration after unregister

Overview

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

net/packet: avoid fanout hook re-registration after unregister

packet_set_ring() temporarily detaches a socket from packet delivery while reconfiguring its ring. It records the previous running state, clears po->num, unregisters the protocol hook when needed, drops po->bind_lock, and later restores po->num and re-registers the hook from the saved was_running value.

That unlocked window can race with NETDEV_UNREGISTER. The notifier can observe the socket as not running, skip __unregister_prot_hook(), and invalidate the per-socket binding by setting po->ifindex to -1 and clearing po->prot_hook.dev. A one-member fanout group can still retain its shared fanout hook device pointer. When packet_set_ring() resumes, re-registering solely from the stale was_running state can re-add the fanout hook after the device has been unregistered.

Treat po->ifindex == -1 as an invalidated binding after reacquiring po->bind_lock. This is distinct from ifindex 0, the normal unbound/wildcard state: ifindex -1 marks an existing device binding that was invalidated when the device was unregistered. Restore po->num as before, but do not re-register the hook if device unregister already detached the socket.

Affected

• Linux >= dc99f600698dcac69b8f56dda9a8a00d645c5ffc < acb40ebfa5c4d62f84339fcbf713f2a9fd033a71
• Linux >= dc99f600698dcac69b8f56dda9a8a00d645c5ffc < c820f4b7f2fa38f8769db0d0cefdd94e2721504d
• Linux >= dc99f600698dcac69b8f56dda9a8a00d645c5ffc < 4628efbdc7affd094181f5263e65c1062e31f15f
• Linux >= dc99f600698dcac69b8f56dda9a8a00d645c5ffc < 80ec024d53a05c60ad1d08968dcf745f10c1665c
• Linux >= dc99f600698dcac69b8f56dda9a8a00d645c5ffc < 0a052e0808e015e68144a9877e6ef42b952c49fa
• Linux >= dc99f600698dcac69b8f56dda9a8a00d645c5ffc < 1bc55c29cd85818e9052f17deb287d5a11fb817f
• Linux >= dc99f600698dcac69b8f56dda9a8a00d645c5ffc < a885387dae7986a55bae5c77a15bdd447f64e9b9
• Linux >= dc99f600698dcac69b8f56dda9a8a00d645c5ffc < 50aff80475abd3533eef4320477037e6fcc6b56e
• Linux 3.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.