Am 09.01.20 um 00:05 schrieb Jens Axboe: > On 1/8/20 4:03 PM, Stefan Metzmacher wrote: >> Am 08.01.20 um 23:53 schrieb Jens Axboe: >>> On 1/8/20 10:04 AM, Stefan Metzmacher wrote: >>>> Am 08.01.20 um 17:40 schrieb Jens Axboe: >>>>> On 1/8/20 9:32 AM, Stefan Metzmacher wrote: >>>>>> Am 08.01.20 um 17:20 schrieb Jens Axboe: >>>>>>> On 1/8/20 6:05 AM, Stefan Metzmacher wrote: >>>>>>>> Hi Jens, >>>>>>>> >>>>>>>>> This works just like openat(2), except it can be performed async. For >>>>>>>>> the normal case of a non-blocking path lookup this will complete >>>>>>>>> inline. If we have to do IO to perform the open, it'll be done from >>>>>>>>> async context. >>>>>>>> >>>>>>>> Did you already thought about the credentials being used for the async >>>>>>>> open? The application could call setuid() and similar calls to change >>>>>>>> the credentials of the userspace process/threads. In order for >>>>>>>> applications like samba to use this async openat, it would be required >>>>>>>> to specify the credentials for each open, as we have to multiplex >>>>>>>> requests from multiple user sessions in one process. >>>>>>>> >>>>>>>> This applies to non-fd based syscall. Also for an async connect >>>>>>>> to a unix domain socket. >>>>>>>> >>>>>>>> Do you have comments on this? >>>>>>> >>>>>>> The open works like any of the other commands, it inherits the >>>>>>> credentials that the ring was setup with. Same with the memory context, >>>>>>> file table, etc. There's currently no way to have multiple personalities >>>>>>> within a single ring. >>>>>> >>>>>> Ah, it's user = get_uid(current_user()); and ctx->user = user in >>>>>> io_uring_create(), right? >>>>> >>>>> That's just for the accounting, it's the: >>>>> >>>>> ctx->creds = get_current_cred(); >>>> >>>> Ok, I just looked at an old checkout. >>>> >>>> In kernel-dk-block/for-5.6/io_uring-vfs I see this only used in >>>> the async processing. Does a non-blocking openat also use ctx->creds? >>> >>> There's basically two sets here - one set is in the ring, and the other >>> is the identity that the async thread (briefly) assumes if we have to go >>> async. Right now they are the same thing, and hence we don't need to >>> play any tricks off the system call submitting SQEs to assume any other >>> identity than the one we have. >> >> I see two cases using it io_sq_thread() and >> io_wq_create()->io_worker_handle_work() call override_creds(). >> >> But aren't non-blocking syscall executed in the context of the thread >> calling io_uring_enter()->io_submit_sqes()? >> In only see some magic around ctx->sqo_mm for that case, but ctx->creds >> doesn't seem to be used in that case. And my design would require that. > > For now, the sq thread (which is used if you use IORING_SETUP_SQPOLL) > currently requires fixed files, so it can't be used with open at the > moment anyway. But if/when enabled, it'll assume the same credentials > as the async context and syscall path. I'm sorry, but I'm still unsure we're talking about the same thing (or maybe I'm missing some basics here). My understanding of the io_uring_enter() is that it will execute as much non-blocking calls as it can without switching to any other kernel thread. And my fear is that openat will use get_current_cred() instead of ctx->creds. I'm I missing something? Thanks! metze
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