Re: [PATCH 4/4] nfc: Avoid endless loops caused by repeated llcp_sock_connect()(Internet mail)

[Xiaoming Ni]

On 2021/3/3 17:28, kiyin(尹亮) wrote:
> 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...

I didn't find the code to modify sk->sk_state after a connect failure. 
Can you provide guidance?

Based on my understanding of the current code:
After llcp_sock_connect() is invoked using the meaningless service_name 
as the parameter, sk->sk_state is set to LLCP_CONNECTING. After that, no 
corresponding service responds to the request because the service_name 
is meaningless, the value of sk->sk_state remains unchanged.
Therefore, when llcp_sock_connect() is invoked again, resources such as 
llcp_sock->service_name are not repeatedly applied because sk_state is 
set to LLCP_CONNECTING.

In this way, the repeated invoking of llcp_sock_connect() does not 
repeatedly leak resources.

Thanks
Xiaoming Ni


> > -----Original Message-----
> > From: Xiaoming Ni [mailto:nixiaoming@xxxxxxxxxx]
> > Sent: Wednesday, March 3, 2021 2:17 PM
> > To: linux-kernel@xxxxxxxxxxxxxxx; kiyin(尹亮) <kiyin@xxxxxxxxxxx>;
> > stable@xxxxxxxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; sameo@xxxxxxxxxxxxxxx;
> > linville@xxxxxxxxxxxxx; davem@xxxxxxxxxxxxx; kuba@xxxxxxxxxx;
> > mkl@xxxxxxxxxxxxxx; stefan@xxxxxxxxxxxxxxxxxx;
> > matthieu.baerts@xxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx
> > Cc: nixiaoming@xxxxxxxxxx; wangle6@xxxxxxxxxx; xiaoqian9@xxxxxxxxxx
> > 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@xxxxxxxxxxx>
> > Link: https://www.openwall.com/lists/oss-security/2020/11/01/1
> > Cc: <stable@xxxxxxxxxxxxxxx> #v3.11
> > Signed-off-by: Xiaoming Ni <nixiaoming@xxxxxxxxxx>
> > ---
> >   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