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.

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/2c260a24cf1c4d30ea3646124f766ee46169280b
• https://git.kernel.org/stable/c/335c8f1566d8e44c384d16b450a18554896d4e8b
• https://git.kernel.org/stable/c/91e61dd7a0af660408e87372d8330ceb218be302
• https://git.kernel.org/stable/c/ab67c2fd3d070a21914d0c31319d3858ab4e199c
• https://git.kernel.org/stable/c/d72e126e9a36d3d33889829df8fc90100bb0e071
• https://git.kernel.org/stable/c/ef21007a7b581c7fe64d5a10c320880a033c837b