From: John Fastabend <john.fastabend@gmail.com>
Date: Mon, 2 Apr 2018 12:50:52 -0700
Subject: bpf: sockmap, duplicates release calls may NULL sk_prot
Patch-mainline: v4.17-rc1
Git-commit: 0e94d87fcfc81883b72574a5cc4638bd87adbb10
References: bsc#1109837

It is possible to have multiple ULP tcp_release call paths in flight
if a sock is closed and simultaneously being removed from the sockmap
control path. The result would be setting the sk_prot to the saved
values on the first iteration and then on the second iteration setting
the value to NULL.

This patch resolves this by ensuring we only reset the sk_prot pointer
if we have a valid saved state to set.

Fixes: 4f738adba30a7 ("bpf: create tcp_bpf_ulp allowing BPF to monitor socket TX/RX data")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 kernel/bpf/sockmap.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -182,8 +182,10 @@ static void bpf_tcp_release(struct sock
 		psock->cork = NULL;
 	}
 
-	sk->sk_prot = psock->sk_proto;
-	psock->sk_proto = NULL;
+	if (psock->sk_proto) {
+		sk->sk_prot = psock->sk_proto;
+		psock->sk_proto = NULL;
+	}
 out:
 	rcu_read_unlock();
 }