On Thursday 03 December 2015 12:26:34 Lee Jones wrote:
> > >
> > > +static ssize_t rproc_state_write(struct file *filp, const char __user *userbuf,
> > > + size_t count, loff_t *ppos)
> > > +{
> > > + struct rproc *rproc = filp->private_data;
> > > + char buf[10];
> > > + int ret;
> > > +
> > > + if (count > sizeof(buf))
> > > + return count;
> > > + ret = copy_from_user(buf, userbuf, count);
> > > + if (ret)
> > > + return -EFAULT;
> > > +
> > > + if (buf[count - 1] == '\n')
> > > + buf[count - 1] = '\0';
> >
> > I believe you can get here with count = 0.
>
> I'm pretty sure you can't.
>
> If you are sure that you can, if you can provide me with a way of
> testing, I'd be happy to put in provisions.
>
I think that a zero-length write() from user space ends up in the write
file operation.
Also, we get a gcc warning about the out-of-bounds access for code like
this, and checking that count is larger than zero avoids the warning.
Arnd
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