Re: [PATCH v6 28/28] ntsync: No longer depend on BROKEN.

[Arnd Bergmann]

On Thu, Dec 12, 2024, at 05:52, kernel test robot wrote:
> Hi Elizabeth,
>
> kernel test robot noticed the following build errors:
>
> [auto build test ERROR on cdd30ebb1b9f36159d66f088b61aee264e649d7a]
>
> url:    
> https://github.com/intel-lab-lkp/linux/commits/Elizabeth-Figura/ntsync-Introduce-NTSYNC_IOC_WAIT_ANY/20241210-031155
> base:   cdd30ebb1b9f36159d66f088b61aee264e649d7a

> All errors (new ones prefixed by >>):
>
>    In file included from include/linux/spinlock.h:60,
>                     from include/linux/wait.h:9,
>                     from include/linux/wait_bit.h:8,
>                     from include/linux/fs.h:6,
>                     from drivers/misc/ntsync.c:11:
>    In function 'check_copy_size',
>        inlined from 'copy_from_user' at include/linux/uaccess.h:207:7,
>        inlined from 'setup_wait' at drivers/misc/ntsync.c:903:6:
>>> include/linux/thread_info.h:259:25: error: call to '__bad_copy_to' declared with attribute error: copy destination size is too small
>      259 |                         __bad_copy_to();
>          |                         ^~~~~~~~~~~~~~~

I looked up the function from the github URL above and found

	int fds[NTSYNC_MAX_WAIT_COUNT + 1];
	const __u32 count = args->count;
	struct ntsync_q *q;
	__u32 total_count;
	__u32 i, j;

	if (args->pad || (args->flags & ~NTSYNC_WAIT_REALTIME))
		return -EINVAL;

	if (args->count > NTSYNC_MAX_WAIT_COUNT)
		return -EINVAL;

	total_count = count;
	if (args->alert)
		total_count++;

	if (copy_from_user(fds, u64_to_user_ptr(args->objs),
			   array_size(count, sizeof(*fds))))
		return -EFAULT;

which looks correct to me, as it has appropriate
range checking on args->count, but I can see how
the warning may be a result of checking 'args->count'
instead of 'count'.

      Arnd