Re: [PATCH 8/8] xen/hvc: replace BUG_ON() with negative return value

[Juergen Gross]

On 13.05.21 12:25, Greg Kroah-Hartman wrote:
> On Thu, May 13, 2021 at 12:03:02PM +0200, Juergen Gross wrote:
> > Xen frontends shouldn't BUG() in case of illegal data received from
> > their backends. So replace the BUG_ON()s when reading illegal data from
> > the ring page with negative return values.
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> >   drivers/tty/hvc/hvc_xen.c | 15 +++++++++++++--
> >   1 file changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
> > index 92c9a476defc..30d7ffb1e04c 100644
> > --- a/drivers/tty/hvc/hvc_xen.c
> > +++ b/drivers/tty/hvc/hvc_xen.c
> > @@ -86,6 +86,11 @@ static int __write_console(struct xencons_info *xencons,
> >   	cons = intf->out_cons;
> >   	prod = intf->out_prod;
> >   	mb();			/* update queue values before going on */
> > +
> > +	if (WARN_ONCE((prod - cons) > sizeof(intf->out),
> > +		      "Illegal ring page indices"))
> > +		return -EINVAL;
>
> How nice, you just rebooted on panic-on-warn systems :(
>
> > +
> >   	BUG_ON((prod - cons) > sizeof(intf->out));
>
> Why keep this line?

Failed to delete it, sorry.

> Please just fix this up properly, if userspace can trigger this, then
> both the WARN_ON() and BUG_ON() are not correct and need to be correctly
> handled.

It can be triggered by the console backend, but I agree a WARN isn't the
way to go here.


Juergen

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