linux-kernel - Re: [PATCH] tty: serial: owl: Fix data race in owl_uart

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Message-ID: <YNLfxMZZ0a80qKLg@hovoldconsulting.com>
Date:   Wed, 23 Jun 2021 09:16:20 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Saubhik Mukherjee <saubhik.mukherjee@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, jirislaby@...nel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        ldv-project@...uxtesting.org, andrianov@...ras.ru
Subject: Re: [PATCH] tty: serial: owl: Fix data race in owl_uart_remove

On Wed, Jun 23, 2021 at 11:06:53AM +0530, Saubhik Mukherjee wrote:
> On 6/17/21 4:52 PM, Greg KH wrote:
> > On Thu, Jun 17, 2021 at 04:34:43PM +0530, Saubhik Mukherjee wrote:
> >> Suppose the driver is registered and a UART port is added. Once an
> >> application opens the port, owl_uart_startup is called which registers
> >> the interrupt handler owl_uart_irq.
> >>
> >> We could have the following race condition:
> >>
> >> When device is removed, owl_uart_remove is called, which calls
> >> uart_remove_one_port, which calls owl_uart_release_port, which writes
> >> NULL to port->membase. At this point parallely, an interrupt could be
> >> handled by owl_uart_irq which reads port->membase.
> >>
> >> This is because it is possible to remove device without closing a port.
> >> Thus, we need to check it and call owl_uart_shutdown in owl_uart_remove.

No, this makes no sense at all. The port is deregistered and hung up by
uart_remove_one_port() (and the interrupt line is consequently disabled
by the driver) before it is released so this can never happen.

> >> Found by Linux Driver Verification project (linuxtesting.org).

And you clearly did not test this, which you should mention.

Johan