Re: [net-next 1/2] dummy: add device MTU validation check

2017-09-21, 08:02:18 -0700, Eric Dumazet wrote:

On Thu, 2017-09-21 at 21:32 +0800, Zhang Shengju wrote:

quoted

Currently, any mtu value can be assigned when adding a new dummy device:
[~]# ip link add name dummy1 mtu 100000 type dummy
[~]# ip link show dummy1
15: dummy1: <BROADCAST,NOARP> mtu 100000 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether 0a:61:6b:16:14:ce brd ff:ff:ff:ff:ff:ff

This patch adds device MTU validation check.

What is wrong with big MTU on dummy ?

It looks like the "centralize MTU checking" series broke that, but
only for changing the MTU on an existing dummy device. Commit
a52ad514fdf3 defined min_mtu/max_mtu in ether_setup, which dummy uses,
but there was no MTU check in dummy prior to that commit.

If this is a generic rule, this check should belong in core network
stack.

quoted

Signed-off-by: Zhang Shengju <redacted>
---
 drivers/net/dummy.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/dummy.c b/drivers/net/dummy.c
index e31ab3b..0276b2b 100644
--- a/drivers/net/dummy.c
+++ b/drivers/net/dummy.c

@@ -365,6 +365,14 @@ static int dummy_validate(struct nlattr *tb[], struct nlattr *data[],
 		if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
 			return -EADDRNOTAVAIL;
 	}
+
+	if (tb[IFLA_MTU]) {
+		u32 mtu = nla_get_u32(tb[IFLA_MTU]);

You do not verify/validate nla_len(tb[IFLA_MTU]).

I think ifla_policy already performs that check:


static const struct nla_policy ifla_policy[IFLA_MAX+1] = {
[...]
	[IFLA_MTU]		= { .type = NLA_U32 },


static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
			struct netlink_ext_ack *extack)
{
[...]
	err = nlmsg_parse(nlh, sizeof(*ifm), tb, IFLA_MAX, ifla_policy, extack);


-- 
Sabrina