[PATCH 5.2 06/66] ipv6: rt6_check should return NULL if from is NULL

[Greg Kroah-Hartman]

From: David Ahern <dsah...@gmail.com>

[ Upstream commit 49d05fe2c9d1b4a27761c9807fec39b8155bef9e ]

Paul reported that l2tp sessions were broken after the commit referenced
in the Fixes tag. Prior to this commit rt6_check returned NULL if the
rt6_info 'from' was NULL - ie., the dst_entry was disconnected from a FIB
entry. Restore that behavior.

Fixes: 93531c674315 ("net/ipv6: separate handling of FIB entries from dst based 
routes")
Reported-by: Paul Donohue <linux-ker...@paulsd.com>
Tested-by: Paul Donohue <linux-ker...@paulsd.com>
Signed-off-by: David Ahern <dsah...@gmail.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/ipv6/route.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2215,7 +2215,7 @@ static struct dst_entry *rt6_check(struc
 {
        u32 rt_cookie = 0;
 
-       if ((from && !fib6_get_cookie_safe(from, &rt_cookie)) ||
+       if (!from || !fib6_get_cookie_safe(from, &rt_cookie) ||
            rt_cookie != cookie)
                return NULL;