Am 30.01.20 um 15:11 schrieb Jens Axboe: > On 1/30/20 3:26 AM, Christian Brauner wrote: >> On Thu, Jan 30, 2020 at 11:11:58AM +0100, Jann Horn wrote: >>> On Thu, Jan 30, 2020 at 2:08 AM Jens Axboe <axboe@xxxxxxxxx> 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@xxxxxxxxx> 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? >>> >>> At the moment, I personally am just interested in this from the >>> perspective of being able to audit the state of personalities, to make >>> important information about the security state of processes visible. >>> >>> Good point about verbosity in fdinfo - I'm not sure about that myself either. >>> >>>> Here's the test app for personality: >>> >>> Oh, that was quick... >>> >>>> # cat 3 >>>> pos: 0 >>>> flags: 02000002 >>>> mnt_id: 14 >>>> user-files: 0 >>>> user-bufs: 0 >>>> personalities: >>>> 1: uid=0/gid=0 >>>> >>>> >>>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>>> index c5ca84a305d3..0b2c7d800297 100644 >>>> --- a/fs/io_uring.c >>>> +++ b/fs/io_uring.c >>>> @@ -6511,6 +6505,45 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit, >>>> return submitted ? submitted : ret; >>>> } >>>> >>>> +struct ring_show_idr { >>>> + struct io_ring_ctx *ctx; >>>> + struct seq_file *m; >>>> +}; >>>> + >>>> +static int io_uring_show_cred(int id, void *p, void *data) >>>> +{ >>>> + struct ring_show_idr *r = data; >>>> + const struct cred *cred = p; >>>> + >>>> + seq_printf(r->m, "\t%5d: uid=%u/gid=%u\n", id, cred->uid.val, >>>> + cred->gid.val); >>> >>> As Stefan said, the ->uid and ->gid aren't very useful, since when a >>> process switches UIDs for accessing things in the filesystem, it >>> probably only changes its EUID and FSUID, not its RUID. >>> I think what's particularly relevant for uring would be the ->fsuid >>> and the ->fsgid along with ->cap_effective; and perhaps for some >>> operations also the ->euid and ->egid. The real UID/GID aren't really >>> relevant when performing normal filesystem operations and such. >> >> This should probably just use the same format that is found in >> /proc/<pid>/status to make it easy for tools to use the same parsing >> logic and for the sake of consistency. We've adapted the same format for >> pidfds. So that would mean: >> >> Uid: 1000 1000 1000 1000 >> Gid: 1000 1000 1000 1000 >> >> Which would be: Real, effective, saved set, and filesystem {G,U}IDs >> >> And CapEff in /proc/<pid>/status has the format: >> CapEff: 0000000000000000 > > I agree, consistency is good. I've added this, and also changed the > naming to be CamelCase, which is seems like most of them are. Now it > looks like this: > > pos: 0 > flags: 02000002 > mnt_id: 14 > UserFiles: 0 > UserBufs: 0 > Personalities: > 1 > Uid: 0 0 0 0 > Gid: 0 0 0 0 > Groups: 0 > CapEff: 0000003fffffffff > > for a single personality registered (root). I have to indent it an extra > tab to display each personality. That looks good. Maybe also print some details of struct io_ring_ctx, flags and the ring sizes, ctx->cred. Maybe details for io_wq and sqo_thread. Maybe pending requests? I'm not sure about how io_wq threads work in detail. Is it possible that a large number of blocking request (against an external harddisk with disconnected cable) to block other blocking requests to a working ssd? It would be good to diagnose such situations from the output. How is this supposed to be ABI-wise? Is it possible to change the output in later kernel versions? metze
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