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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, Cong Wang <xiyou.wangcong@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        syzbot+5e5e969e525129229052@syzkaller.appspotmail.com
Subject: [PATCH 4.20 014/145] net/wan: fix a double free in x25_asy_open_tty()
Date:   Mon,  7 Jan 2019 13:30:51 +0100
Message-Id: <20190107104439.234661171@linuxfoundation.org>
In-Reply-To: <20190107104437.308206189@linuxfoundation.org>
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4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Cong Wang <xiyou.wangcong@gmail.com>

[ Upstream commit d5c7c745f254c6cb98b3b3f15fe789b8bd770c72 ]

When x25_asy_open() fails, it already cleans up by itself,
so its caller doesn't need to free the memory again.

It seems we still have to call x25_asy_free() to clear the SLF_INUSE
bit, so just set these pointers to NULL after kfree().

Reported-and-tested-by: syzbot+5e5e969e525129229052@syzkaller.appspotmail.com
Fixes: 3b780bed3138 ("x25_asy: Free x25_asy on x25_asy_open() failure.")
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>
---
 drivers/net/wan/x25_asy.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/net/wan/x25_asy.c
+++ b/drivers/net/wan/x25_asy.c
@@ -485,8 +485,10 @@ static int x25_asy_open(struct net_devic
 
 	/* Cleanup */
 	kfree(sl->xbuff);
+	sl->xbuff = NULL;
 noxbuff:
 	kfree(sl->rbuff);
+	sl->rbuff = NULL;
 norbuff:
 	return -ENOMEM;
 }