CVE-2024-36489

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

tls: fix missing memory barrier in tls_init

In tls_init(), a write memory barrier is missing, and store-store

reordering may cause NULL dereference in tls_{setsockopt,getsockopt}.

CPU0 CPU1

----- -----

// In tls_init()

// In tls_ctx_create()

ctx = kzalloc()

ctx->sk_proto = READ_ONCE(sk->sk_prot) -(1)

// In update_sk_prot()

WRITE_ONCE(sk->sk_prot, tls_prots) -(2)

// In sock_common_setsockopt()

READ_ONCE(sk->sk_prot)->setsockopt()

// In tls_{setsockopt,getsockopt}()

ctx->sk_proto->setsockopt() -(3)

In the above scenario, when (1) and (2) are reordered, (3) can observe

the NULL value of ctx->sk_proto, causing NULL dereference.

To fix it, we rely on rcu_assign_pointer() which implies the release

barrier semantic. By moving rcu_assign_pointer() after ctx->sk_proto is

initialized, we can ensure that ctx->sk_proto are visible when

changing sk->sk_prot.