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

Hi Kees

On 2020-07-10 3:44 p.m., Kees Cook wrote:

On Fri, Jul 10, 2020 at 03:10:25PM -0700, Scott Branden wrote:

quoted

On 2020-07-10 3:04 p.m., Matthew Wilcox wrote:

quoted

On Fri, Jul 10, 2020 at 02:00:32PM -0700, Scott Branden wrote:

quoted

quoted

@@ -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,
Scott