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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jianlin Shi <jishi@redhat.com>,
        Hangbin Liu <liuhangbin@gmail.com>,
        David Ahern <dsahern@gmail.com>,
        Jakub Kicinski <jakub.kicinski@netronome.com>
Subject: [PATCH 5.4 186/191] ipv6/addrconf: only check invalid header values when NETLINK_F_STRICT_CHK is set
Date:   Thu,  2 Jan 2020 23:07:48 +0100
Message-Id: <20200102215849.500783837@linuxfoundation.org>
In-Reply-To: <20200102215829.911231638@linuxfoundation.org>
References: <20200102215829.911231638@linuxfoundation.org>
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From: Hangbin Liu <liuhangbin@gmail.com>

[ Upstream commit 2beb6d2901a3f73106485d560c49981144aeacb1 ]

In commit 4b1373de73a3 ("net: ipv6: addr: perform strict checks also for
doit handlers") we add strict check for inet6_rtm_getaddr(). But we did
the invalid header values check before checking if NETLINK_F_STRICT_CHK
is set. This may break backwards compatibility if user already set the
ifm->ifa_prefixlen, ifm->ifa_flags, ifm->ifa_scope in their netlink code.

I didn't move the nlmsg_len check because I thought it's a valid check.

Reported-by: Jianlin Shi <jishi@redhat.com>
Fixes: 4b1373de73a3 ("net: ipv6: addr: perform strict checks also for doit handlers")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/addrconf.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5231,16 +5231,16 @@ static int inet6_rtm_valid_getaddr_req(s
 		return -EINVAL;
 	}
 
+	if (!netlink_strict_get_check(skb))
+		return nlmsg_parse_deprecated(nlh, sizeof(*ifm), tb, IFA_MAX,
+					      ifa_ipv6_policy, extack);
+
 	ifm = nlmsg_data(nlh);
 	if (ifm->ifa_prefixlen || ifm->ifa_flags || ifm->ifa_scope) {
 		NL_SET_ERR_MSG_MOD(extack, "Invalid values in header for get address request");
 		return -EINVAL;
 	}
 
-	if (!netlink_strict_get_check(skb))
-		return nlmsg_parse_deprecated(nlh, sizeof(*ifm), tb, IFA_MAX,
-					      ifa_ipv6_policy, extack);
-
 	err = nlmsg_parse_deprecated_strict(nlh, sizeof(*ifm), tb, IFA_MAX,
 					    ifa_ipv6_policy, extack);
 	if (err)