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Miller" , Eric Dumazet , Julian Anastasov , Hangbin Liu Subject: [PATCHv4 net 1/2] ipv4/icmp: fix rt dst dev null pointer dereference Date: Thu, 22 Aug 2019 22:19:48 +0800 Message-Id: <20190822141949.29561-2-liuhangbin@gmail.com> X-Mailer: git-send-email 2.19.2 In-Reply-To: <20190822141949.29561-1-liuhangbin@gmail.com> References: <20190815060904.19426-1-liuhangbin@gmail.com> <20190822141949.29561-1-liuhangbin@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org In __icmp_send() there is a possibility that the rt->dst.dev is NULL, e,g, with tunnel collect_md mode, which will cause kernel crash. Here is what the code path looks like, for GRE: - ip6gre_tunnel_xmit - ip6gre_xmit_ipv4 - __gre6_xmit - ip6_tnl_xmit - if skb->len - t->tun_hlen - eth_hlen > mtu; return -EMSGSIZE - icmp_send - net = dev_net(rt->dst.dev); <-- here The reason is __metadata_dst_init() init dst->dev to NULL by default. We could not fix it in __metadata_dst_init() as there is no dev supplied. On the other hand, the reason we need rt->dst.dev is to get the net. So we can just try get it from skb->dev when rt->dst.dev is NULL. v4: Julian Anastasov remind skb->dev also could be NULL. We'd better still use dst.dev and do a check to avoid crash. v3: No changes. v2: fix the issue in __icmp_send() instead of updating shared dst dev in {ip_md, ip6}_tunnel_xmit. Fixes: c8b34e680a09 ("ip_tunnel: Add tnl_update_pmtu in ip_md_tunnel_xmit") Signed-off-by: Hangbin Liu --- net/ipv4/icmp.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c index 1510e951f451..001f03f76bc4 100644 --- a/net/ipv4/icmp.c +++ b/net/ipv4/icmp.c @@ -582,7 +582,13 @@ void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info, if (!rt) goto out; - net = dev_net(rt->dst.dev); + + if (rt->dst.dev) + net = dev_net(rt->dst.dev); + else if (skb_in->dev) + net = dev_net(skb_in->dev); + else + goto out; /* * Find the original header. It is expected to be valid, of course. -- 2.19.2