Re: [PATCH v2 net] hv_sock: Fix hang when a connection is closed

[David Miller <davem@davemloft.net>]

From: Dexuan Cui <decui@microsoft.com>
Date: Wed, 31 Jul 2019 01:25:45 +0000

> 
> 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 <decui@microsoft.com>

Applied and queued up for -stable.

Do not ever CC: stable for networking patches, we submit to -stable manually.

Thank you.