CVE-2026-64459

Status: UPDATED  |  Advisory ID: CVE-2026-64459

Key Details

Affected Products, Subsystems & Sectors

What to Know

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

tcp: restore RCU grace period in tcp_ao_destroy_sock

Commit 51e547e8c89c ("tcp: Free TCP-AO/TCP-MD5 info/keys without RCU")

removed the call_rcu() callback from tcp_ao_destroy_sock(), arguing that

"the destruction of info/keys is delayed until the socket destructor"

and therefore "no one can discover it anymore".

That argument does not hold for the call site in tcp_connect()

(net/ipv4/tcp_output.c:4327-4332). At that point the socket is in

TCP_SYN_SENT, has already been inserted into the inet ehash by

inet_hash_connect() in tcp_v4_connect(), and is therefore very much

discoverable: any softirq running tcp_v4_rcv() on another CPU can take

the socket out of the ehash, walk into tcp_inbound_hash(), and load

tp->ao_info via implicit RCU before bh_lock_sock_nested() is taken on

the destroying CPU.

The reader path then enters __tcp_ao_do_lookup() (net/ipv4/tcp_ao.c:208)

which re-loads tp->ao_info via rcu_dereference_check(); the re-load can

still observe the (about-to-be-freed) pointer because there is no

synchronize_rcu() between rcu_assign_pointer(tp->ao_info, NULL) and

tcp_ao_info_free() in tcp_ao_destroy_sock(). The captured pointer is

then walked at line 223:

hlist_for_each_entry_rcu(key, &ao->head, node, ...)

The writer's synchronous kfree() is free to complete between the line

218 re-fetch and the line 223 hlist iteration. The slab is reused

(or simply LIST_POISON1-stamped if not yet reused) and the iteration

walks attacker-controlled or poison memory in softirq context.

Reproducer (no debug shim, stock x86_64 v7.1-rc2 SMP+KASAN, QEMU+KVM):

an unprivileged uid=1000 process inside CLONE_NEWUSER|CLONE_NEWNET

installs TCP_MD5SIG + TCP_AO_ADD_KEY on a TCP socket, sprays forged

TCP-AO segments toward its eventual 4-tuple via raw sockets, then

calls connect(). The md5-wins reconciliation in tcp_connect() fires

tcp_ao_destroy_sock(); the softirq backlog reader on the loopback

NAPI path crashes on the freed ao->head.first walk:

Oops: general protection fault, probably for non-canonical

address 0xfbd59c000000002f

KASAN: maybe wild-memory-access in range

[0xdead000000000178-0xdead00000000017f]

CPU: 0 UID: 1000 PID: 100 Comm: repro_userns

RIP: 0010:__tcp_ao_do_lookup+0x107/0x1c0

Call Trace: <IRQ>

__tcp_ao_do_lookup+0x107/0x1c0

tcp_ao_inbound_lookup.constprop.0+0x12a/0x200

tcp_inbound_ao_hash+0x5ea/0x1520

tcp_inbound_hash+0x7ce/0x1240

tcp_v4_rcv+0x1e7a/0x3e10

...

Restore the RCU grace period: re-add struct rcu_head to tcp_ao_info

and replace the synchronous tcp_ao_info_free() with a call_rcu()

callback. Readers that captured tp->ao_info before rcu_assign_pointer

NULLed it now see the object remain valid until rcu_read_unlock().

With the patch applied the reproducer runs cleanly for 2000 iterations

on the same kernel build. (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References