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

[Jens Axboe <axboe@kernel.dk>]

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.

-- 
Jens Axboe