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

[Kees Cook <keescook@chromium.org>]

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. :)

-- 
Kees Cook