From dd17277c2483db588c470df406f63059f3975432 Mon Sep 17 00:00:00 2001 From: Dexuan Cui Date: Wed, 31 Jul 2019 01:25:45 +0000 Subject: [PATCH] hv_sock: Fix hang when a connection is closed [ Upstream commit 685703b497bacea8765bb409d6b73455b73c540e ] There is a race condition for an established connection that is being closed by the guest: the refcnt is 4 at the end of hvs_release() (Note: here the 'remove_sock' is false): 1 for the initial value; 1 for the sk being in the bound list; 1 for the sk being in the connected list; 1 for the delayed close_work. After hvs_release() finishes, __vsock_release() -> sock_put(sk) *may* decrease the refcnt to 3. Concurrently, hvs_close_connection() runs in another thread: calls vsock_remove_sock() to decrease the refcnt by 2; call sock_put() to decrease the refcnt to 0, and free the sk; next, the "release_sock(sk)" may hang due to use-after-free. In the above, after hvs_release() finishes, if hvs_close_connection() runs faster than "__vsock_release() -> sock_put(sk)", then there is not any issue, because at the beginning of hvs_close_connection(), the refcnt is still 4. The issue can be resolved if an extra reference is taken when the connection is established. Fixes: a9eeb998c28d ("hv_sock: Add support for delayed close") Signed-off-by: Dexuan Cui Reviewed-by: Sunil Muthuswamy Signed-off-by: David S. Miller Signed-off-by: Sasha Levin --- net/vmw_vsock/hyperv_transport.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c index 52ac3e49c7ef..ec72a5edaa1b 100644 --- a/net/vmw_vsock/hyperv_transport.c +++ b/net/vmw_vsock/hyperv_transport.c @@ -320,6 +320,11 @@ static void hvs_close_connection(struct vmbus_channel *chan) lock_sock(sk); hvs_do_close_lock_held(vsock_sk(sk), true); release_sock(sk); + + /* Release the refcnt for the channel that's opened in + * hvs_open_connection(). + */ + sock_put(sk); } static void hvs_open_connection(struct vmbus_channel *chan) @@ -389,6 +394,9 @@ static void hvs_open_connection(struct vmbus_channel *chan) } set_per_channel_state(chan, conn_from_host ? new : sk); + + /* This reference will be dropped by hvs_close_connection(). */ + sock_hold(conn_from_host ? new : sk); vmbus_set_chn_rescind_callback(chan, hvs_close_connection); /* Set the pending send size to max packet size to always get -- 2.20.1