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Date:   Sat,  8 Aug 2020 13:06:52 -0400
From:   Gaurav Singh <gaurav1086@...il.com>
To:     gaurav1086@...il.com, "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>, Shaohua Li <shli@...com>,
        netdev@...r.kernel.org (open list:NETWORKING [IPv4/IPv6]),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] [net/ipv6] ip6_output: Add ipv6_pinfo null check

This PR fixes a possible segmentation violation.

In function: ip6_xmit(), we have
const struct ipv6_pinfo *np = inet6_sk(sk); which returns NULL
unconditionally (regardless sk being  NULL or not).

In include/linux/ipv6.h:

static inline struct ipv6_pinfo * inet6_sk(const struct sock *__sk)
{
    return NULL;
}

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

Thereafter, 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() that accesses np without check which
may cause a segment violation.

Fixes: 513674b5a2c9c ("net: reevalulate autoflowlabel setting after sysctl setting")

Signed-off-by: Gaurav Singh <gaurav1086@...il.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

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