Messages in this thread | | | Date | Thu, 18 Oct 2018 02:23:32 +1100 | From | Aleksa Sarai <> | Subject | Re: [PATCH v3 0/3] namei: implement various lookup restriction AT_* flags |
| |
On 2018-10-09, Aleksa Sarai <cyphar@cyphar.com> wrote: > The need for some sort of control over VFS's path resolution (to avoid > malicious paths resulting in inadvertent breakouts) has been a very > long-standing desire of many userspace applications. This patchset is a > revival of Al Viro's old AT_NO_JUMPS[1,2] patchset (which was a variant > of David Drysdale's O_BENEATH patchset[3] which was a spin-off of the > Capsicum project[4]) with a few additions and changes made based on the > previous discussion within [5] as well as others I felt were useful.
I've been thinking about this problem a little more (from the UX side of things) and I have a feeling that adding 5 different O_* flags related to resolution -- rather than properties related to opening the file -- might be less than ideal (even though, as discussed in previous threads, there is a need for these flags and for them to be separated).
There is *some* precedence for this with O_PATH[**] changing fairly large semantics of openat(2) but there are some things about O_PATH which I think could be improved.
What if we had a resolveat(2) which acted like openat(..., O_PATH) *but* it allowed us to have new flags and to separate the scoping flags from the (fairly limited) space of O_* flags. Then O_PATH could effectively just be a legacy way of doing resolveat(2) -- with only O_CLOEXEC, O_DIRECTORY, and O_NOFOLLOW support.
And the main things we could add would be:
* These resolution flags, with only support available from resolveat(2) for the moment. The idea would be that AT_EMPTY_PATH would be the recommended way to make use of this.
* Support for RESOLVE_{NOPERM,RDONLY,WRONLY,RDWR} (which after some discussions with Eric last year might be necessary in order to make /proc/$pid/fd/$fd re-opening of O_PATH descriptors safer -- which is something that we use in both runc and LXC).
Is this idea palatable, or was this something considered during the development of O_PATH and someone had an argument why augmenting O_PATH is better than a new syscall?
[**] And while writing this paragraph I noticed that I didn't update the O_PATH "flag whitelist" to allow the scoping flags to affect it. I will include a fix for this in v4 (I must've lost it in an early rebase before I sent v1).
-- Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH <https://www.cyphar.com/> [unhandled content-type:application/pgp-signature] | |