On Tue, Sep 25, 2018 at 09:50:18AM -0600, Shuah Khan wrote:
> >>> Also can you run this test as normal user?
> >>
> >> No. Must be run as root to open /dev/watchdog. When /dev/watchdog is opened, the
> >> WD is started and if not updated properly, the system will crash.
> >
> > Hmm. I don't understand why the system would panic if non-root user can't open the
> > device, at least in the context of this test.
> >
> > fd = open("/dev/watchdog", O_WRONLY);
> >
> > if (fd == -1) {
> > printf("Watchdog device not enabled.\n");
> > exit(-1);
> > }
> >
> >
> > Shouldn't it just exit based on the code above?
> >
> >>
> >
> >> "cat /dev/watchdog" is one of my favorite ways to crash a system. :) :)
> >
> > That doesn't sound great, if a non-root user can bring the system down!!
> >
>
> This got me concerned enough that I tried this with softdog. It behaved just
> the way I expected it.
>
> cat /dev/watchdog
> cat: /dev/watchdog: Permission denied
>
> Running the test as non-root does the following as per the current logic.
>
> watchdog-test -b
> Watchdog device not enabled.
>
> I think this logic could be improved to detect that a non-root user is running
> the test and print appropriate message.
>
> However, I am not seeing the behavior you are describing that "cat /dev/watchdog"
> panics the syste. Did you mean running a root which is expected unless you terminate
> before the timeout? If you are seeing this as non-root user on you system, the
> watchdog driver could be suspect.
>
> thanks,
> -- Shuah
Sorry, for misunderstanding. Let me rephrase:
When you asked if the test can be run as a normal user::
No. The test must be run as root to open /dev/watchdog as the permission
on /dev/watchdog allow only root to open it. The reason that we only
allow root to open /dev/watchdog is that it is trivial to crash
the system. Just open /dev/watchdog and don't update the watchdog.
One of my favorite ways to crash the system is to
as root "cat /dev/watchdog."
--
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Jerry Hoemann Software Engineer Hewlett Packard Enterprise
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