[PATCH] io_uring: enable audit and restrict cred override for IORING_OP_FIXED_FD_INSTALL

[Jens Axboe]

On 1/23/24 3:40 PM, Jens Axboe wrote:
> On 1/23/24 3:35 PM, Jens Axboe wrote:
>>
>> On Tue, 23 Jan 2024 16:55:02 -0500, Paul Moore wrote:
>>> We need to correct some aspects of the IORING_OP_FIXED_FD_INSTALL
>>> command to take into account the security implications of making an
>>> io_uring-private file descriptor generally accessible to a userspace
>>> task.
>>>
>>> The first change in this patch is to enable auditing of the FD_INSTALL
>>> operation as installing a file descriptor into a task's file descriptor
>>> table is a security relevant operation and something that admins/users
>>> may want to audit.
>>>
>>> [...]
>>
>> Applied, thanks!
>>
>> [1/1] io_uring: enable audit and restrict cred override for IORING_OP_FIXED_FD_INSTALL
>>       commit: 16bae3e1377846734ec6b87eee459c0f3551692c
> 
> So after doing that and writing the test case and testing it, it dawned
> on me that we should potentially allow the current task creds. And to
> make matters worse, this is indeed what happens if eg the application
> would submit this with IOSQE_ASYNC or if it was part of a linked series
> and we marked it async.
> 
> While I originally reasoned for why this is fine as it'd be silly to
> register your current creds and then proceed to pass in that personality,
> I do think that we should probably handle that case and clearly separate
> the case of "we assigned creds from the submitting task because we're
> handing it to a thread" vs "the submitting task asked for other creds
> that were previously registered".
> 
> I'll take a look and see what works the best here.

Actually, a quick look and it's fine, the usual async offload will do
the right thing. So let's just keep it as-is, I don't think there's any
point to complicating this for some theoretically-valid-but-obscure use
case!

FWIW, the test case is here, and I'll augment it now to add IOSQE_ASYNC
as well just to cover all the bases.

https://git.kernel.dk/cgit/liburing/commit/?id=bc576ca398661b266d3e4a4f5db3a9cf7f33fe62

-- 
Jens Axboe