CVE-2026-74496fou: Fix use-after-free in fou_create()

Official description

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 packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/0ee628a58d83e571f36ec9f07624d6845e420c50
• https://git.kernel.org/stable/c/a6fca682cfa2041e31aa72cc397c4a1406eb7468
• https://git.kernel.org/stable/c/b3f9c3e60aa25453774f899d25b5e61dd0bec1d5
• https://git.kernel.org/stable/c/99f4d3120b244f92e5df787152041296a2860cb5
• https://git.kernel.org/stable/c/58835985c035a8333742f829ad7e0889a082f9d3
• https://git.kernel.org/stable/c/9042867d4701728f0c6527215b11471759904d8f
• https://git.kernel.org/stable/c/a28d8903bfe76089ea4bbdbff9976965f9ef8107
• https://git.kernel.org/stable/c/b14361aca6350ff7907b0e9903c7b94dc7d5d4a0