linux-kernel - Re: general protection fault in tomoyo_socket_sendmsg

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Date:   Sat, 13 Feb 2021 11:10:30 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Shuah Khan <skhan@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Valentina Manea <valentina.manea.m@...il.com>,
        syzkaller-bugs@...glegroups.com, Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+95ce4b142579611ef0a9@...kaller.appspotmail.com>
Subject: Re: general protection fault in tomoyo_socket_sendmsg_permission

On Sat, Feb 13, 2021 at 07:02:22PM +0900, Tetsuo Handa wrote:
> Greg, will you queue https://lkml.kernel.org/r/20210205135707.4574-1-penguin-kernel@I-love.SAKURA.ne.jp (which can
> close a report which is wasting syzbot's resource with 5300+ crashes) for 5.12 ? The change shown below will be
> too large to test before merge window for 5.12 opens. 
> 
> The patch for fixing "general protection fault in tomoyo_socket_sendmsg_permission" will kill kthread_get_run().
> Closing frequently crashing bug now is the better.
> 
> On 2021/02/11 22:40, Tetsuo Handa wrote:
> > I guess that we need to serialize attach operation and reset/detach operations, for
> > it seems there is a race window that might result in "general protection fault in
> > tomoyo_socket_sendmsg_permission". Details follows...
> 
> Here is untested diff that is expected to be complete.
> 
> (1) Handle kthread_create() failure (which avoids "KASAN: null-ptr-deref Write in vhci_shutdown_connection")
>     by grouping socket lookup, SOCK_STREAM check and kthread_get_run() into usbip_prepare_threads() function.
> 
> (2) Serialize usbip_sockfd_store(), detach_store(), attach_store(), usbip_sockfd_store() and
>     ud->eh_ops.shutdown()/ud->eh_ops.reset()/ud->eh_ops.unusable() operations using usbip_store_mutex mutex
>     (which avoids "general protection fault in tomoyo_socket_sendmsg_permission").
> 
> (3) Don't reset ud->tcp_socket to NULL in vhci_device_reset(). Since tx_thread/rx_thread depends on
>     ud->tcp_socket != NULL whereas tcp_socket and tx_thread/rx_thread are assigned at the same time,
>     it is never safe to reset only ud->tcp_socket from ud->eh_ops.reset(). And actually nobody is
>     calling ud->eh_ops.reset() without ud->eh_ops.shutdown().
> 
> (4) usbip_sockfd_store() must perform {sdev,udc}->ud.status != SDEV_ST_AVAILABLE && {sdev,udc}->ud.status = SDEV_ST_USED
>     exclusively, or multiple tx_thread/rx_thread can be created when concurrently called. Although (2) will already
>     serialize this action, (1) will make it possible to perform within one spinlock section.

Shouldn't this be 4 different patches?

thanks,

greg k-h