net: don't clear sock->sk early to avoid trouble in strparser

af_inet sets sock->sk to NULL which trips strparser over:

BUG: kernel NULL pointer dereference, address: 0000000000000012
PGD 0 P4D 0
Oops: 0000 [#1] SMP PTI
CPU: 7 PID: 0 Comm: swapper/7 Not tainted 5.2.0-rc1-00139-g14629453a6d3 #21
RIP: 0010:tcp_peek_len+0x10/0x60
RSP: 0018:ffffc02e41c54b98 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff9cf924c4e030 RCX: 0000000000000051
RDX: 0000000000000000 RSI: 000000000000000c RDI: ffff9cf97128f480
RBP: ffff9cf9365e0300 R08: ffff9cf94fe7d2c0 R09: 0000000000000000
R10: 000000000000036b R11: ffff9cf939735e00 R12: ffff9cf91ad9ae40
R13: ffff9cf924c4e000 R14: ffff9cf9a8fcbaae R15: 0000000000000020
FS: 0000000000000000(0000) GS:ffff9cf9af7c0000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000012 CR3: 000000013920a003 CR4: 00000000003606e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
 <IRQ>
 strp_data_ready+0x48/0x90
 tls_data_ready+0x22/0xd0 [tls]
 tcp_rcv_established+0x569/0x620
 tcp_v4_do_rcv+0x127/0x1e0
 tcp_v4_rcv+0xad7/0xbf0
 ip_protocol_deliver_rcu+0x2c/0x1c0
 ip_local_deliver_finish+0x41/0x50
 ip_local_deliver+0x6b/0xe0
 ? ip_protocol_deliver_rcu+0x1c0/0x1c0
 ip_rcv+0x52/0xd0
 ? ip_rcv_finish_core.isra.20+0x380/0x380
 __netif_receive_skb_one_core+0x7e/0x90
 netif_receive_skb_internal+0x42/0xf0
 napi_gro_receive+0xed/0x150
 nfp_net_poll+0x7a2/0xd30 [nfp]
 ? kmem_cache_free_bulk+0x286/0x310
 net_rx_action+0x149/0x3b0
 __do_softirq+0xe3/0x30a
 ? handle_irq_event_percpu+0x6a/0x80
 irq_exit+0xe8/0xf0
 do_IRQ+0x85/0xd0
 common_interrupt+0xf/0xf
 </IRQ>
RIP: 0010:cpuidle_enter_state+0xbc/0x450

To avoid this issue set sock->sk after sk_prot->close.
My grepping and testing did not discover any code which
would depend on the current behaviour.

Fixes: c46234ebb4 ("tls: RX path for ktls")
Reported-by: David Beckett <david.beckett@netronome.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/af_inet.c

@@ -428,8 +428,8 @@ int inet_release(struct socket *sock)
 		if (sock_flag(sk, SOCK_LINGER) &&
 		    !(current->flags & PF_EXITING))
 			timeout = sk->sk_lingertime;
-		sock->sk = NULL;
 		sk->sk_prot->close(sk, timeout);
+		sock->sk = NULL;
 	}
 	return 0;
 }