Re: [PATCH 2/4] fs: Remove FIRMWARE_PREALLOC_BUFFER from kernel_read_file() enums

Kees Cook
2020-07-16T21:16:16Z

On Thu, Jul 16, 2020 at 01:35:17PM -0700, Scott Branden wrote:
> On 2020-07-10 3:44 p.m., Kees Cook wrote:
> > On Fri, Jul 10, 2020 at 03:10:25PM -0700, Scott Branden wrote:
> > >
> > > On 2020-07-10 3:04 p.m., Matthew Wilcox wrote:
> > > > On Fri, Jul 10, 2020 at 02:00:32PM -0700, Scott Branden wrote:
> > > > > > @@ -950,8 +951,8 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
> > > > > > goto out;
> > > > > > }
> > > > > > - if (id != READING_FIRMWARE_PREALLOC_BUFFER)
> > > > > > - *buf = vmalloc(i_size);
> > > > > > + if (!*buf)
> > > > > The assumption that *buf is always NULL when id !=
> > > > > READING_FIRMWARE_PREALLOC_BUFFER doesn't appear to be correct.
> > > > > I get unhandled page faults due to this change on boot.
> > > > Did it give you a stack backtrace?
> > > Yes, but there's no requirement that *buf need to be NULL when calling this
> > > function.
> > > To fix my particular crash I added the following locally:
> > >
> > > --- a/kernel/module.c
> > > +++ b/kernel/module.c
> > > @@ -3989,7 +3989,7 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char
> > > __user *, uargs, int, flags)
> > >  {
> > >      struct load_info info = { };
> > >      loff_t size;
> > > -    void *hdr;
> > > +    void *hdr = NULL;
> > >      int err;
> > >
> > >      err = may_init_module();
> > Thanks for the diagnosis and fix! I haven't had time to cycle back
> > around to this series yet. Hopefully soon. :)
> >
> In order to assist in your patchset I have combined it with my patch series
> here:
> https://github.com/sbranden/linux/tree/kernel_read_file_for_kees
>
> Please let me know if this matches your expectations for my patches or if
> there is something else I need to change.

Thanks! I was working on the next revision of this last night, and I'm
trying to get through today's email to finish it. I'll take a look!

--
Kees Cook