linux-kernel - RE: [PATCH 4/4] nfc: Avoid endless loops caused by repeated llcp_sock

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Date:   Wed, 3 Mar 2021 09:28:11 +0000
From:   kiyin(尹亮) <kiyin@...cent.com>
To:     Xiaoming Ni <nixiaoming@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "sameo@...ux.intel.com" <sameo@...ux.intel.com>,
        "linville@...driver.com" <linville@...driver.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "mkl@...gutronix.de" <mkl@...gutronix.de>,
        "stefan@...enfreihafen.org" <stefan@...enfreihafen.org>,
        "matthieu.baerts@...sares.net" <matthieu.baerts@...sares.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "wangle6@...wei.com" <wangle6@...wei.com>,
        "xiaoqian9@...wei.com" <xiaoqian9@...wei.com>
Subject: RE: [PATCH 4/4] nfc: Avoid endless loops caused by repeated
 llcp_sock_connect()(Internet mail)

Hi xiaoming,
  the path can only fix the endless loop problem. it can't fix the meaningless llcp_sock->service_name problem.
  if we set llcp_sock->service_name to meaningless string, the connect will be failed. and sk->sk_state will not be LLCP_CONNECTED. then we can call llcp_sock_connect() many times. that leaks everything: llcp_sock->dev, llcp_sock->local, llcp_sock->ssap, llcp_sock->service_name...

Regards,
kiyin.

> -----Original Message-----
> From: Xiaoming Ni [mailto:nixiaoming@...wei.com]
> Sent: Wednesday, March 3, 2021 2:17 PM
> To: linux-kernel@...r.kernel.org; kiyin(尹亮) <kiyin@...cent.com>;
> stable@...r.kernel.org; gregkh@...uxfoundation.org; sameo@...ux.intel.com;
> linville@...driver.com; davem@...emloft.net; kuba@...nel.org;
> mkl@...gutronix.de; stefan@...enfreihafen.org;
> matthieu.baerts@...sares.net; netdev@...r.kernel.org
> Cc: nixiaoming@...wei.com; wangle6@...wei.com; xiaoqian9@...wei.com
> Subject: [PATCH 4/4] nfc: Avoid endless loops caused by repeated
> llcp_sock_connect()(Internet mail)
> 
> When sock_wait_state() returns -EINPROGRESS, "sk->sk_state" is
> LLCP_CONNECTING. In this case, llcp_sock_connect() is repeatedly invoked,
>  nfc_llcp_sock_link() will add sk to local->connecting_sockets twice.
>  sk->sk_node->next will point to itself, that will make an endless loop  and
> hang-up the system.
> To fix it, check whether sk->sk_state is LLCP_CONNECTING in
>  llcp_sock_connect() to avoid repeated invoking.
> 
> fix CVE-2020-25673
> Fixes: b4011239a08e ("NFC: llcp: Fix non blocking sockets connections")
> Reported-by: "kiyin(尹亮)" <kiyin@...cent.com>
> Link: https://www.openwall.com/lists/oss-security/2020/11/01/1
> Cc: <stable@...r.kernel.org> #v3.11
> Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>
> ---
>  net/nfc/llcp_sock.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/nfc/llcp_sock.c b/net/nfc/llcp_sock.c index
> 59172614b249..a3b46f888803 100644
> --- a/net/nfc/llcp_sock.c
> +++ b/net/nfc/llcp_sock.c
> @@ -673,6 +673,10 @@ static int llcp_sock_connect(struct socket *sock,
> struct sockaddr *_addr,
>  		ret = -EISCONN;
>  		goto error;
>  	}
> +	if (sk->sk_state == LLCP_CONNECTING) {
> +		ret = -EINPROGRESS;
> +		goto error;
> +	}
> 
>  	dev = nfc_get_device(addr->dev_idx);
>  	if (dev == NULL) {
> --
> 2.27.0
>