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

[Scott Branden]

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)
Â{
ÂÂÂÂ struct load_info info = { };
ÂÂÂÂ loff_t size;
-ÂÂÂ void *hdr;
+ÂÂÂ void *hdr = NULL;
ÂÂÂÂ int err;

ÂÂÂÂ err = may_init_module();
>