Re: [PATCH 1/1] nfc: llcp: reject connect() on sockets not in LLCP_CLOSED state

[Simon Horman <horms@kernel.org>]

On Fri, Sep 18, 2026 at 11:39:20AM +0800, Yuchao Zhang wrote:
> When a socket is bound via llcp_sock_bind(), its state transitions to
> LLCP_BOUND and it is linked into the local->sockets hlist via
> nfc_llcp_sock_link().
> 
> Currently, llcp_sock_connect() only checks if the socket is already
> connected (LLCP_CONNECTED) or in progress (LLCP_CONNECTING):
> 
> 	if (sk->sk_state == LLCP_CONNECTED) {
> 		ret = -EISCONN;
> 		goto error;
> 	}
> 	if (sk->sk_state == LLCP_CONNECTING) {
> 		ret = -EINPROGRESS;
> 		goto error;
> 	}
> 
> Crucially, it does not check for the LLCP_BOUND (or LLCP_LISTEN) state.
> Previous fixes addressing CVE-2020-25670 / CVE-2020-25673 added the check
> for LLCP_CONNECTING to prevent duplicate in-flight connection attempts
> from corrupting the connecting_sockets list. However, they assumed any
> other non-connected socket was in LLCP_CLOSED, leaving the LLCP_BOUND
> state window unhandled.
> 
> If connect() is invoked on a socket that has already been bound:
> 1. llcp_sock_connect() silently overwrites llcp_sock->dev and
>    llcp_sock->local without releasing previous references or freeing the
>    bound service_name, leading to refcount and memory leaks.
> 2. The socket remains linked in local->sockets, while llcp_sock_connect()
>    links it again into local->connecting_sockets via nfc_llcp_sock_link().
> 3. When connection confirmation (CC) arrives, nfc_llcp_recv_cc() executes:
> 
> 	nfc_llcp_sock_unlink(&local->connecting_sockets, sk);
> 	nfc_llcp_sock_link(&local->sockets, sk);
> 
>    Because sk was never unlinked from local->sockets, the head.first of
>    local->sockets still points to &sk->sk_node. The second
>    hlist_add_head() sets sk->sk_node.next = sk->sk_node, producing a
>    self-referential loop. Subsequent traversals of local->sockets
>    (e.g. nfc_llcp_sock_get(), nfc_llcp_socket_release()) enter an
>    infinite loop with spinlocks held, resulting in kernel soft-lockups.
> 4. Furthermore, if connect() specifies a different NFC device index than
>    bind(), the socket remains linked on device A's socket list while
>    being assigned to device B, causing cross-device socket confusion.
> 
> Fix this by ensuring that llcp_sock_connect() only accepts sockets in the
> LLCP_CLOSED state, returning -EBADFD otherwise, matching the state check
> behavior in llcp_sock_bind().
> 
> Fixes: d646960f7986 ("NFC: Initial LLCP support")
> Signed-off-by: Yuchao Zhang <ndaugoing@gmail.com>

Reviewed-by: Simon Horman <horms@kernel.org>