linux-kernel - [PATCH ipsec] xfrm: fix rcu lock in xfrm_notify

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Message-Id: <20210922085006.13570-1-nicolas.dichtel@6wind.com>
Date:   Wed, 22 Sep 2021 10:50:06 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     steffen.klassert@...unet.com,
        syzbot+3d9866419b4aa8f985d6@...kaller.appspotmail.com
Cc:     davem@...emloft.net, herbert@...dor.apana.org.au, kuba@...nel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        netdev@...r.kernel.org, Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: [PATCH ipsec] xfrm: fix rcu lock in xfrm_notify_userpolicy()

As stated in the comment above xfrm_nlmsg_multicast(), rcu read lock must
be held before calling this function.

Reported-by: syzbot+3d9866419b4aa8f985d6@...kaller.appspotmail.com
Fixes: 703b94b93c19 ("xfrm: notify default policy on update")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
---
 net/xfrm/xfrm_user.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 0eba0c27c665..3a3cb09eec12 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -1967,6 +1967,7 @@ static int xfrm_notify_userpolicy(struct net *net)
 	int len = NLMSG_ALIGN(sizeof(*up));
 	struct nlmsghdr *nlh;
 	struct sk_buff *skb;
+	int err;
 
 	skb = nlmsg_new(len, GFP_ATOMIC);
 	if (skb == NULL)
@@ -1988,7 +1989,11 @@ static int xfrm_notify_userpolicy(struct net *net)
 
 	nlmsg_end(skb, nlh);
 
-	return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_POLICY);
+	rcu_read_lock();
+	err = xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_POLICY);
+	rcu_read_unlock();
+
+	return err;
 }
 
 static int xfrm_set_default(struct sk_buff *skb, struct nlmsghdr *nlh,
-- 
2.33.0