On 28/01/2020 22:42, Jens Axboe wrote: > On 1/28/20 11:04 AM, Jens Axboe wrote: >> On 1/28/20 10:19 AM, Jens Axboe wrote: >>> On 1/28/20 9:19 AM, Jens Axboe wrote: >>>> On 1/28/20 9:17 AM, Stefan Metzmacher wrote: >>> OK, so here are two patches for testing: >>> >>> https://git.kernel.dk/cgit/linux-block/log/?h=for-5.6/io_uring-vfs-creds >>> >>> #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'll try and write a test case for this just to see if it actually works, >>> so far it's totally untested. >>> >>> Adding Pavel to the CC. >> >> Minor tweak to ensuring we do the right thing for async offload as well, >> and it tests fine for me. Test case is: >> >> - Run as root >> - Register personality for root >> - create root only file >> - check we can IORING_OP_OPENAT the file >> - switch to user id test >> - check we cannot IORING_OP_OPENAT the file >> - check that we can open the file with IORING_OP_USE_CREDS linked > > 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. > To be honest, sounds pretty dangerous. Especially since somebody started talking about stealing fds from a process, it could lead to a nasty loophole somehow. E.g. root registers its credentials, passes io_uring it to non-privileged children, and then some process steals the uring fd (though, it would need priviledged mode for code-injection or else). Could we Cc here someone really keen on security? Stefan, could you please explain, how this 5 syscalls pattern from the first email came in the first place? Just want to understand the case. -- Pavel Begunkov
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