Re: [RFC PATCH 2/9] audit,io_uring,io-wq: add some basic audit support to io_uring

Pavel Begunkov
2021-06-03T10:40:37Z

On 6/2/21 4:46 PM, Richard Guy Briggs wrote:
> On 2021-06-02 09:26, Pavel Begunkov wrote:
>> On 5/28/21 5:02 PM, Paul Moore wrote:
>>> On Wed, May 26, 2021 at 4:19 PM Paul Moore <paul@paul-moore.com> wrote:
>>>> ... If we moved the _entry
>>>> and _exit calls into the individual operation case blocks (quick
>>>> openat example below) so that only certain operations were able to be
>>>> audited would that be acceptable assuming the high frequency ops were
>>>> untouched? My initial gut feeling was that this would involve >50% of
>>>> the ops, but Steve Grubb seems to think it would be less; it may be
>>>> time to look at that a bit more seriously, but if it gets a NACK
>>>> regardless it isn't worth the time - thoughts?
>>>>
>>>> case IORING_OP_OPENAT:
>>>> audit_uring_entry(req->opcode);
>>>> ret = io_openat(req, issue_flags);
>>>> audit_uring_exit(!ret, ret);
>>>> break;
>>>
>>> I wanted to pose this question again in case it was lost in the
>>> thread, I suspect this may be the last option before we have to "fix"
>>> things at the Kconfig level. I definitely don't want to have to go
>>> that route, and I suspect most everyone on this thread feels the same,
>>> so I'm hopeful we can find a solution that is begrudgingly acceptable
>>> to both groups.
>>
>> May work for me, but have to ask how many, and what is the
>> criteria? I'd think anything opening a file or manipulating fs:
>>
>> IORING_OP_ACCEPT, IORING_OP_CONNECT, IORING_OP_OPENAT[2],
>> IORING_OP_RENAMEAT, IORING_OP_UNLINKAT, IORING_OP_SHUTDOWN,
>> IORING_OP_FILES_UPDATE
>> + coming mkdirat and others.
>>
>> IORING_OP_CLOSE? IORING_OP_SEND IORING_OP_RECV?
>>
>> What about?
>> IORING_OP_FSYNC, IORING_OP_SYNC_FILE_RANGE,
>> IORING_OP_FALLOCATE, IORING_OP_STATX,
>> IORING_OP_FADVISE, IORING_OP_MADVISE,
>> IORING_OP_EPOLL_CTL
>>
>>
>> Another question, io_uring may exercise asynchronous paths,
>> i.e. io_issue_sqe() returns before requests completes.
>> Shouldn't be the case for open/etc at the moment, but was that
>> considered?
>
> This would be why audit needs to monitor a thread until it wraps up, to
> wait for the result code. My understanding is that both sync and async
> parts of an op would be monitored.

There may be a misunderstanding

audit_start(req)
ret = io_issue_sqe(req);
audit_end(ret);

io_issue_sqe() may return 0 but leave the request inflight,
which will be completed asynchronously e.g. by IRQ, not going
through io_issue_sqe() or any io_read()/etc helpers again, and
after last audit_end() had already happened.
That's the case with read/write/timeout, but is not true for
open/etc.

>> I don't see it happening, but would prefer to keep it open
>> async reimplementation in a distant future. Does audit sleep?
>
> Some parts do, some parts don't depending on what they are interacting
> with in the kernel. It can be made to not sleep if needed.

Ok, good

--
Pavel Begunkov