Re: [PATCH for-next v2 1/1] io_uring/rsrc: disallow multi-source reg buffers

[Pavel Begunkov <asml.silence@gmail.com>]

On 2/21/23 16:29, Jens Axboe wrote:
> On 2/20/23 7:53 AM, Gabriel Krisman Bertazi wrote:
>> Pavel Begunkov <asml.silence@gmail.com> writes:
>>
>>> If two or more mappings go back to back to each other they can be passed
>>> into io_uring to be registered as a single registered buffer. That would
>>> even work if mappings came from different sources, e.g. it's possible to
>>> mix in this way anon pages and pages from shmem or hugetlb. That is not
>>> a problem but it'd rather be less prone if we forbid such mixing.
>>>
>>> Cc: <stable@vger.kernel.org>
>>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>>> ---
>>>   io_uring/rsrc.c | 15 ++++++++-------
>>>   1 file changed, 8 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
>>> index a59fc02de598..70d7f94670f9 100644
>>> --- a/io_uring/rsrc.c
>>> +++ b/io_uring/rsrc.c
>>> @@ -1162,18 +1162,19 @@ struct page **io_pin_pages(unsigned long ubuf, unsigned long len, int *npages)
>>>   	pret = pin_user_pages(ubuf, nr_pages, FOLL_WRITE | FOLL_LONGTERM,
>>>   			      pages, vmas);
>>>   	if (pret == nr_pages) {
>>> +		struct file *file = vmas[0]->vm_file;
>>> +
>>>   		/* don't support file backed memory */
>>>   		for (i = 0; i < nr_pages; i++) {
>>> -			struct vm_area_struct *vma = vmas[i];
>>> -
>>> -			if (vma_is_shmem(vma))
>>> +			if (vmas[i]->vm_file != file)
>>> +				break;
>>
>> Perhaps, return -EINVAL instead of -EOPNOTSUPP
> 
> Agree, -EOPNOTSUPP is OK for an unsupported case, but I think
> -EINVAL makes more sense for the weird case of mixed sources
> as it's unlikely to ever make sense to support that.

ok

-- 
Pavel Begunkov