netdev - [PATCH 3/8] ip_tunnel: Clamp MTU to bounds on new link

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 29 Mar 2018 09:11:15 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     David Miller <davem@...emloft.net>
CC:     Herbert Xu <herbert@...dor.apana.org.au>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        <netdev@...r.kernel.org>
Subject: [PATCH 3/8] ip_tunnel: Clamp MTU to bounds on new link

From: Stefano Brivio <sbrivio@...hat.com>

Otherwise, it's possible to specify invalid MTU values directly
on creation of a link (via 'ip link add'). This is already
prevented on subsequent MTU changes by commit b96f9afee4eb
("ipv4/6: use core net MTU range checking").

Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
Signed-off-by: Stefano Brivio <sbrivio@...hat.com>
Acked-by: Sabrina Dubroca <sd@...asysnail.net>
Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
---
 net/ipv4/ip_tunnel.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index 6d21068f9b55..7c76dd17b6b9 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -1108,8 +1108,14 @@ int ip_tunnel_newlink(struct net_device *dev, struct nlattr *tb[],
 		eth_hw_addr_random(dev);
 
 	mtu = ip_tunnel_bind_dev(dev);
-	if (!tb[IFLA_MTU])
+	if (tb[IFLA_MTU]) {
+		unsigned int max = 0xfff8 - dev->hard_header_len - nt->hlen;
+
+		dev->mtu = clamp(dev->mtu, (unsigned int)ETH_MIN_MTU,
+				 (unsigned int)(max - sizeof(struct iphdr)));
+	} else {
 		dev->mtu = mtu;
+	}
 
 	ip_tunnel_add(itn, nt);
 out:
-- 
2.14.1