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 Christian
