Re: [PATCH v1] drivers/vhost/vhost: fix overflow checks in vhost_overflow

[Daniil Tatianin]

On 12/7/22 6:01 PM, Michael S. Tsirkin wrote:
> On Wed, Dec 07, 2022 at 04:46:31PM +0300, Daniil Tatianin wrote:
> > The if statement would erroneously check for > ULONG_MAX, which could
> > never evaluate to true. Check for equality instead.
> >
> > Found by Linux Verification Center (linuxtesting.org) with the SVACE
> > static analysis tool.
> >
> > Signed-off-by: Daniil Tatianin <d-tatianin@xxxxxxxxxxxxxx>
>
> It can trigger on a 32 bit system. I'd also expect more analysis
> of the code flow than "this can not trigger switch to a condition
> that can" to accompany a patch.

Oops, my bad. It can trigger on 32 bit indeed. Sorry, completely 
overlooked that.

Thanks

> > ---
> >   drivers/vhost/vhost.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index 40097826cff0..8df706e7bc6c 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -730,7 +730,7 @@ static bool log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
> >   /* Make sure 64 bit math will not overflow. */
> >   static bool vhost_overflow(u64 uaddr, u64 size)
> >   {
> > -	if (uaddr > ULONG_MAX || size > ULONG_MAX)
> > +	if (uaddr == ULONG_MAX || size == ULONG_MAX)
> >   		return true;
> >   
> >   	if (!size)
> > --
> > 2.25.1