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

[Jens Axboe]

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.

-- 
Jens Axboe