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

Scott Branden
2020-07-16T20:35:48Z

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:
>>
>> 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,
Scott