[Bug 217613] New: [BUG] [media] dvb-usb: possible data-inconsistency due to data races in dib0700_rc_query_old_firmware()

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=217613

            Bug ID: 217613
           Summary: [BUG] [media] dvb-usb: possible data-inconsistency due
                    to data races in dib0700_rc_query_old_firmware()
           Product: Drivers
           Version: 2.5
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: USB
          Assignee: drivers_usb@kernel-bugs.kernel.org
          Reporter: islituo@gmail.com
        Regression: No

Our static analysis tool finds some possible data races in the
DVB USB driver in Linux 6.4.0.

The variable d->priv->buf is often accessed with holding the
lock d->usb_mutex, here is an example:

  dib0700_change_protocol()  --> Line 638 in dib0700_core.c
    st = d->priv;  --> Line 641 in dib0700_core.c (Alias)
    mutex_lock_interruptible(&d->usb_mutex)
               --> Line 644 in dib0700_core.c (Lock d->usb_mutex)
    st->buf[0] = REQUEST_SET_RC;
               --> Line 649 in dib0700_core.c (Access d->priv->buf)

However, in the function dib0700_rc_query_old_firmware(), the
variable d->priv->buf is accessed without holding the lock
d->usb_mutex:

  dib0700_rc_query_old_firmware()  --> Line 516 in dib0700_devices.c
    st = d->priv;  --> Line 522 in dib0700_devices.c (Alias)
    st->buf[0] = REQUEST_POLL_RC;
               --> Line 532 in dib0700_devices.c (Access st->buf)

And thus harmful data races can occur because they can make
data in st-buf inconsistent.

I am not quite sure whether these possible data races are real and
how to fix them if they are real.

Any feedback would be appreciated, thanks!

Reported-by: BassCheck <bass@buaa.edu.cn>

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