Re: IORING_REGISTER_CREDS[_UPDATE]() and credfd_create()?

Jens Axboe
2020-01-30T03:18:37Z

On 1/29/20 7:20 PM, Jens Axboe wrote:
> On 1/29/20 6:08 PM, Jens Axboe wrote:
>> On 1/29/20 10:34 AM, Jens Axboe wrote:
>>> On 1/29/20 7:59 AM, Jann Horn wrote:
>>>> On Tue, Jan 28, 2020 at 8:42 PM Jens Axboe <axboe@kernel.dk> wrote:
>>>>> On 1/28/20 11:04 AM, Jens Axboe wrote:
>>>>>> On 1/28/20 10:19 AM, Jens Axboe wrote:
>>>> [...]
>>>>>>> #1 adds support for registering the personality of the invoking task,
>>>>>>> and #2 adds support for IORING_OP_USE_CREDS. Right now it's limited to
>>>>>>> just having one link, it doesn't support a chain of them.
>>>> [...]
>>>>> I didn't like it becoming a bit too complicated, both in terms of
>>>>> implementation and use. And the fact that we'd have to jump through
>>>>> hoops to make this work for a full chain.
>>>>>
>>>>> So I punted and just added sqe->personality and IOSQE_PERSONALITY.
>>>>> This makes it way easier to use. Same branch:
>>>>>
>>>>> https://git.kernel.dk/cgit/linux-block/log/?h=for-5.6/io_uring-vfs-creds
>>>>>
>>>>> I'd feel much better with this variant for 5.6.
>>>>
>>>> Some general feedback from an inspectability/debuggability perspective:
>>>>
>>>> At some point, it might be nice if you could add a .show_fdinfo
>>>> handler to the io_uring_fops that makes it possible to get a rough
>>>> overview over the state of the uring by reading /proc/$pid/fdinfo/$fd,
>>>> just like e.g. eventfd (see eventfd_show_fdinfo()). It might be
>>>> helpful for debugging to be able to see information about the fixed
>>>> files and buffers that have been registered. Same for the
>>>> personalities; that information might also be useful when someone is
>>>> trying to figure out what privileges a running process actually has.
>>>
>>> Agree, that would be a very useful addition. I'll take a look at it.
>>
>> Jann, how much info are you looking for? Here's a rough start, just
>> shows the number of registered files and buffers, and lists the
>> personalities registered. We could also dump the buffer info for
>> each of them, and ditto for the files. Not sure how much verbosity
>> is acceptable in fdinfo?
>>
>> Here's the test app for personality:
>>
>> # cat 3
>> pos: 0
>> flags: 02000002
>> mnt_id: 14
>> user-files: 0
>> user-bufs: 0
>> personalities:
>> 1: uid=0/gid=0
>
> Here's one that adds the registered buffers and files as well. So
> essentially this shows any info on the registered parts.

Output of this version, using t/io_uring from fio:

# cat /proc/338/fdinfo/4
pos: 0
flags: 02000002
mnt_id: 14
user-files: 1
0: nvme0n1p2
user-bufs: 128
0: 55ea44b52000/4096
1: 55ea44b54000/4096
2: 55ea44b56000/4096
3: 55ea44b58000/4096
4: 55ea44b5a000/4096
5: 55ea44b5c000/4096
6: 55ea44b5e000/4096
7: 55ea44b60000/4096
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--
Jens Axboe