netdev - [PATCH net-next v1] net: mctp: use deprecated parser in mctp_set_link

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Date: Thu, 28 Dec 2023 15:02:58 +0800
From: Lin Ma <linma@....edu.cn>
To: jk@...econstruct.com.au,
	matt@...econstruct.com.au,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Lin Ma <linma@....edu.cn>
Subject: [PATCH net-next v1] net: mctp: use deprecated parser in mctp_set_link_af

In mctp set_link_af implementation `mctp_set_link_af`, it uses strict
parser nla_parse_nested to parse the nested attribute. This is fine in
most cases but not here, as the rtnetlink uses *bad magic* in setlink
code, see code snippet in function `do_setlink`.

  nla_for_each_nested(af, tb[IFLA_AF_SPEC], rem) {
    const struct rtnl_af_ops *af_ops;
    BUG_ON(!(af_ops = rtnl_af_lookup(nla_type(af)))); <= (1)
    err = af_ops->set_link_af(dev, af, extack);       <= (2)

That is, in line (1), the attribute type of af will used to look up the
af_ops, and for MCTP case will use AF_MCTP here to get mctp_af_ops.
Therefore, the attribute with type AF_MCTP will never survive in the
check within the nla_parse_nested.

  if (!(nla->nla_type & NLA_F_NESTED)) {  <= nla_type is AF_MCTP
    NL_SET_ERR_MSG_ATTR(extack, nla, "NLA_F_NESTED is missing");
    return -EINVAL;  <= always invalid
  }

For other set_link_af users IPV4 and IPV6 both make a trick here by
using nla_parse_nested_deprecated, which will check the NLA_F_NESTED
then able to use this type field as family value. This patch simply port
the MCTP code also to deprecated parser to make it work.

Signed-off-by: Lin Ma <linma@....edu.cn>
---
 net/mctp/device.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/mctp/device.c b/net/mctp/device.c
index acb97b257428..226c8e3ed85f 100644
--- a/net/mctp/device.c
+++ b/net/mctp/device.c
@@ -400,8 +400,8 @@ static int mctp_set_link_af(struct net_device *dev, const struct nlattr *attr,
 	struct mctp_dev *mdev;
 	int rc;

-	rc = nla_parse_nested(tb, IFLA_MCTP_MAX, attr, ifla_af_mctp_policy,
-			      NULL);
+	rc = nla_parse_nested_deprecated(tb, IFLA_MCTP_MAX, attr, ifla_af_mctp_policy,
+					 NULL);
 	if (rc)
 		return rc;

-- 
2.17.1