Linux vulnerability

What happened

In the Linux kernel, the following vulnerability has been resolved: fou: Fix use-after-free in fou_create() fou_create() publishes struct fou through sk_user_data before adding the new FOU port to the per-netns list. If fou_add_to_port_list() fails, the error path frees fou while it is still reachable through sk_user_data. A concurrent receive can then dereference the freed object in fou_from_sock(). This ordering issue was previously noted in the linked discussion. The failure is reachable when local port 0 is requested. Each socket binds to a different ephemeral port, but fou_cfg_cmp() compares the requested port 0 and reports -EALREADY once an entry already exists. Release the tunnel socket before freeing fou so sk_user_data is cleared first, and defer reclamation with kfree_rcu() to protect concurrent RCU readers. This matches the lifetime handling in fou_release().

Affected versions

Linux: 23461551c00628c3f3fe9cf837bf53cf8f212b63 through before 0ee628a58d83e571f36ec9f07624d6845e420c50 (git); 23461551c00628c3f3fe9cf837bf53cf8f212b63 through before a6fca682cfa2041e31aa72cc397c4a1406eb7468 (git); 23461551c00628c3f3fe9cf837bf53cf8f212b63 through before b3f9c3e60aa25453774f899d25b5e61dd0bec1d5 (git); 23461551c00628c3f3fe9cf837bf53cf8f212b63 through before 99f4d3120b244f92e5df787152041296a2860cb5 (git); 23461551c00628c3f3fe9cf837bf53cf8f212b63 through before 58835985c035a8333742f829ad7e0889a082f9d3 (git); 23461551c00628c3f3fe9cf837bf53cf8f212b63 through before 9042867d4701728f0c6527215b11471759904d8f (git); 23461551c00628c3f3fe9cf837bf53cf8f212b63 through before a28d8903bfe76089ea4bbdbff9976965f9ef8107 (git); 23461551c00628c3f3fe9cf837bf53cf8f212b63 through before b14361aca6350ff7907b0e9903c7b94dc7d5d4a0 (git); 3.18 Fixed: See vendor advisory.

Why it matters

Review the vendor advisory and exposure of the affected product to determine operational impact.

Detection & mitigation

• Apply vendor-provided updates or mitigations.
• Review affected product exposure and access logs.