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From:   Gaurav Singh <gaurav1086@gmail.com>
To:     gaurav1086@gmail.com, "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Jakub Kicinski <kuba@kernel.org>,
        netdev@vger.kernel.org (open list:NETWORKING [IPv4/IPv6]),
        linux-kernel@vger.kernel.org (open list)
Subject: [PATCH] [net/ipv6] ip6_output: Add ipv6_pinfo null check
Date:   Mon, 27 Jul 2020 22:13:48 -0400
Message-Id: <20200728021348.4116-1-gaurav1086@gmail.com>
In-Reply-To: <20200727033810.28883-1-gaurav1086@gmail.com>
References: <20200727033810.28883-1-gaurav1086@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Add return to fix build issue. Haven't reproduced this issue at
my end. 

My hypothesis is this: In function: ip6_xmit(), we have
const struct ipv6_pinfo *np = inet6_sk(sk); which returns NULL.

Further down the function, there's a check:
if (np) hlimit = hp->htop_limit 

Further, we have a call
ip6_flow_hdr(hdr, tclass, ip6_make_flowlabel(net, skb, fl6->flowlabel,
ip6_autoflowlabel(net, np), fl6)); . 

Hence np = NULL gets passed in
the function ip6_autoflowlabel() which accesses np-> without check which
may cause a segment violation.

Signed-off-by: Gaurav Singh <gaurav1086@gmail.com>
---
 net/ipv6/ip6_output.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 8a8c2d0cfcc8..94a07c9bd925 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -181,10 +181,10 @@ int ip6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 
 bool ip6_autoflowlabel(struct net *net, const struct ipv6_pinfo *np)
 {
-	if (!np->autoflowlabel_set)
-		return ip6_default_np_autolabel(net);
-	else
+	if (np && np->autoflowlabel_set)
 		return np->autoflowlabel;
+	else
+		return ip6_default_np_autolabel(net);
 }
 
 /*
-- 
2.17.1