tls: fix missing memory barrier in tls_init

Vulnerability 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