Vulnerability CVE-2024-36489
Published: 2024-06-21

Description:
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.

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