Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
To:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@zx2c4.com>, stable@vger.kernel.org
Subject: [PATCH] ipv6: Properly check reference count flag before taking reference
Date:   Mon, 23 Sep 2019 16:46:12 +0200
Message-Id: <20190923144612.29668-1-Jason@zx2c4.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

People are reporting that WireGuard experiences erratic crashes on 5.3,
and bisected it down to 7d30a7f6424e. Casually flipping through that
commit I noticed that a flag is checked using `|` instead of `&`, which in
this current case, means that a reference is never incremented, which
would result in the use-after-free users are seeing. This commit changes
the `|` to the proper `&` test.

Cc: stable@vger.kernel.org
Fixes: 7d30a7f6424e ("Merge branch 'ipv6-avoid-taking-refcnt-on-dst-during-route-lookup'")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 net/ipv6/ip6_fib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 87f47bc55c5e..6e2af411cd9c 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -318,7 +318,7 @@ struct dst_entry *fib6_rule_lookup(struct net *net, struct flowi6 *fl6,
 	if (rt->dst.error == -EAGAIN) {
 		ip6_rt_put_flags(rt, flags);
 		rt = net->ipv6.ip6_null_entry;
-		if (!(flags | RT6_LOOKUP_F_DST_NOREF))
+		if (!(flags & RT6_LOOKUP_F_DST_NOREF))
 			dst_hold(&rt->dst);
 	}
 
-- 
2.21.0