From: John Fastabend <john.fastabend@gmail.com>

Date: Thu, 1 Apr 2021 15:00:19 -0700

Subject: bpf, sockmap: Fix sk->prot unhash op reset

Patch-mainline: v5.12-rc7

Git-commit: 1c84b33101c82683dee8b06761ca1f69e78c8ee7

References: bsc#1155518

In '4da6a196f93b1' we fixed a potential unhash loop caused when

a TLS socket in a sockmap was removed from the sockmap. This

happened because the unhash operation on the TLS ctx continued

to point at the sockmap implementation of unhash even though the

psock has already been removed. The sockmap unhash handler when a

psock is removed does the following,

 void sock_map_unhash(struct sock *sk)

 {

	void (*saved_unhash)(struct sock *sk);

	struct sk_psock *psock;

	rcu_read_lock();

	psock = sk_psock(sk);

	if (unlikely(!psock)) {

		rcu_read_unlock();

		if (sk->sk_prot->unhash)

			sk->sk_prot->unhash(sk);

		return;

	}

        [...]

 }

The unlikely() case is there to handle the case where psock is detached

but the proto ops have not been updated yet. But, in the above case

with TLS and removed psock we never fixed sk_prot->unhash() and unhash()

points back to sock_map_unhash resulting in a loop. To fix this we added

this bit of code,

 static inline void sk_psock_restore_proto(struct sock *sk,

                                          struct sk_psock *psock)

 {

       sk->sk_prot->unhash = psock->saved_unhash;

This will set the sk_prot->unhash back to its saved value. This is the

correct callback for a TLS socket that has been removed from the sock_map.

Unfortunately, this also overwrites the unhash pointer for all psocks.

We effectively break sockmap unhash handling for any future socks.

Omitting the unhash operation will leave stale entries in the map if

a socket transition through unhash, but does not do close() op.

To fix set unhash correctly before calling into tls_update. This way the

TLS enabled socket will point to the saved unhash() handler.

Fixes: 4da6a196f93b1 ("bpf: Sockmap/tls, during free we may call tcp_bpf_unhash() in loop")

Reported-by: Cong Wang <xiyou.wangcong@gmail.com>

Reported-by: Lorenz Bauer <lmb@cloudflare.com>

Suggested-by: Cong Wang <xiyou.wangcong@gmail.com>

Signed-off-by: John Fastabend <john.fastabend@gmail.com>

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Link: https://lore.kernel.org/bpf/161731441904.68884.15593917809745631972.stgit@john-XPS-13-9370

Acked-by: Gary Lin <glin@suse.com>

NOTE from Gary:

  * This patch is modified to fit SLE15-SP2.

---

 include/linux/skmsg.h |    8 ++++++--

 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/include/linux/skmsg.h

+++ b/include/linux/skmsg.h

@@ -358,13 +358,17 @@ static inline void sk_psock_update_proto

 static inline void sk_psock_restore_proto(struct sock *sk,

 					  struct sk_psock *psock)

 {

-	sk->sk_prot->unhash = psock->saved_unhash;

-

 	if (psock->sk_proto) {

 		struct inet_connection_sock *icsk = inet_csk(sk);

 		bool has_ulp = !!icsk->icsk_ulp_data;

 		if (has_ulp) {

+			/* TLS does not have an unhash proto in SW cases, but we need

+			 * to ensure we stop using the sock_map unhash routine because

+			 * the associated psock is being removed. So use the original

+			 * unhash handler.

+			 */

+			WRITE_ONCE(sk->sk_prot->unhash, psock->saved_unhash);

 			tcp_update_ulp(sk, psock->sk_proto,

 				       psock->saved_write_space);

 		} else {