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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, Ralf Baechle <ralf@linux-mips.org>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        syzbot+622bdabb128acc33427d@syzkaller.appspotmail.com,
        syzbot+6eaef7158b19e3fec3a0@syzkaller.appspotmail.com,
        syzbot+9399c158fcc09b21d0d2@syzkaller.appspotmail.com,
        syzbot+a34e5f3d0300163f0c87@syzkaller.appspotmail.com
Subject: [PATCH 4.4 094/158] netrom: hold sock when setting skb->destructor
Date:   Fri,  2 Aug 2019 11:28:35 +0200
Message-Id: <20190802092223.511536567@linuxfoundation.org>
In-Reply-To: <20190802092203.671944552@linuxfoundation.org>
References: <20190802092203.671944552@linuxfoundation.org>
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From: Cong Wang <xiyou.wangcong@gmail.com>

[ Upstream commit 4638faac032756f7eab5524be7be56bee77e426b ]

sock_efree() releases the sock refcnt, if we don't hold this refcnt
when setting skb->destructor to it, the refcnt would not be balanced.
This leads to several bug reports from syzbot.

I have checked other users of sock_efree(), all of them hold the
sock refcnt.

Fixes: c8c8218ec5af ("netrom: fix a memory leak in nr_rx_frame()")
Reported-and-tested-by: <syzbot+622bdabb128acc33427d@syzkaller.appspotmail.com>
Reported-and-tested-by: <syzbot+6eaef7158b19e3fec3a0@syzkaller.appspotmail.com>
Reported-and-tested-by: <syzbot+9399c158fcc09b21d0d2@syzkaller.appspotmail.com>
Reported-and-tested-by: <syzbot+a34e5f3d0300163f0c87@syzkaller.appspotmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/netrom/af_netrom.c |    1 +
 1 file changed, 1 insertion(+)

--- a/net/netrom/af_netrom.c
+++ b/net/netrom/af_netrom.c
@@ -968,6 +968,7 @@ int nr_rx_frame(struct sk_buff *skb, str
 
 	window = skb->data[20];
 
+	sock_hold(make);
 	skb->sk             = make;
 	skb->destructor     = sock_efree;
 	make->sk_state	    = TCP_ESTABLISHED;