netdev - [PATCH net] net: dcb: Validate netlink message in DCB handler

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Date:   Tue, 22 Dec 2020 22:49:44 +0100
From:   Petr Machata <me@...chata.org>
To:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Petr Machata <me@...chata.org>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: [PATCH net] net: dcb: Validate netlink message in DCB handler

DCB uses the same handler function for both RTM_GETDCB and RTM_SETDCB
messages. dcb_doit() bounces RTM_SETDCB mesasges if the user does not have
the CAP_NET_ADMIN capability.

However, the operation to be performed is not decided from the DCB message
type, but from the DCB command. Thus DCB_CMD_*_GET commands are used for
reading DCB objects, the corresponding SET and DEL commands are used for
manipulation.

The assumption is that set-like commands will be sent via an RTM_SETDCB
message, and get-like ones via RTM_GETDCB. However, this assumption is not
enforced.

It is therefore possible to manipulate DCB objects without CAP_NET_ADMIN
capability by sending the corresponding command in an RTM_GETDCB message.
That is a bug. Fix it by validating the type of the request message against
the type used for the response.

Fixes: 2f90b8657ec9 ("ixgbe: this patch adds support for DCB to the kernel and ixgbe driver")
Signed-off-by: Petr Machata <me@...chata.org>
---
 net/dcb/dcbnl.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/dcb/dcbnl.c b/net/dcb/dcbnl.c
index 084e159a12ba..7d49b6fd6cef 100644
--- a/net/dcb/dcbnl.c
+++ b/net/dcb/dcbnl.c
@@ -1765,6 +1765,8 @@ static int dcb_doit(struct sk_buff *skb, struct nlmsghdr *nlh,
 	fn = &reply_funcs[dcb->cmd];
 	if (!fn->cb)
 		return -EOPNOTSUPP;
+	if (fn->type != nlh->nlmsg_type)
+		return -EPERM;

 	if (!tb[DCB_ATTR_IFNAME])
 		return -EINVAL;
-- 
2.25.1