Re: [Qemu-devel] [PATCH 5/8] usb: fix unbounded stack for inotify_watchfn

[Peter Xu]

On Tue, Mar 08, 2016 at 01:22:46PM +0100, Paolo Bonzini wrote:
> 
> 
> On 08/03/2016 08:20, Peter Maydell wrote:
> >> > +#define __BUF_LEN (sizeof(struct inotify_event) + NAME_MAX + 1)
> >> >      /* From the man page: atleast one event can be read */
> >> > -    int len = sizeof(struct inotify_event) + NAME_MAX + 1;
> >> >      int pos;
> >> > -    char buf[len];
> >> > +    char buf[__BUF_LEN];
> > The commit message subject says this is fixing an unbounded
> > stack usage, but (a) this array wasn't unbounded in size
> > (b) the change doesn't change the size we allocate.
> > What are you trying to do here?

Sorry. I should be more clear to say "it avoids one warning during
compilation" rather than saying "fix unbounded stack usage", while
it's not.

> 
> I suspect it's just fixing a false positive in the compiler.
> 
> Paolo

Yes. I will avoid touching these kinds of places in the code next
time I guess... only when necessary. Since this one is easy, I'd
like to send another standalone patch, using sizeof(). rather than
macros, to avoid the warning.

Thanks.
Peter