On 04/04/2022 23:28, Linus Torvalds wrote:
On Mon, Apr 4, 2022 at 1:29 PM Mickaël Salaün <mic@xxxxxxxxxxx> wrote:
This initial proposal was using a new faccessat2(2) flag:
AT_INTERPRETED, see
https://lore.kernel.org/all/20200908075956.1069018-2-mic@xxxxxxxxxxx/
What do you think about that? I'm happy to get back to this version if
everyone is OK with it.
I'm certainly happi_er_ with that, but I find that particular patch
odd for other reasons.
In no particular order:
- what's with the insane non-C syntax? Double parentheses have no
actual meaning in C:
if ((flags & AT_INTERPRETED)) {
if ((mode & MAY_EXEC)) {
so I don't understand why you'd use that strance thing.
I guess it comes from a previous version that ANDed two booleans.
- why is this an AT_INTERPRETED flag? I don't understand the name, I
don't understand the semantics.
I wasn't sure it was a good idea to add another mode bit, so I ended up
using a flag to not break compatibility of other mode checks but extend
the semantic to interpreted scripts. But I agree that a new mode makes
sense.
Why would that flag have the same value as AT_SYMLINK_FOLLOW?
It was a bug.
Why isn't this just a new _mode_ bit, which is what I feel is
sensible? We only use three bits (with no bits set meaning
"existence"), so we have *tons* of bits left in that namespace, and it
would make much more sense to me to have
#define EXECVE_OK 8
which is the same as the "group exec" bit, so it actually makes
some kind of sense too.
Looks fine to me. The "EXECVE_" prefix is a bit weird but it will not be
defined in the kernel like X_OK and others anyway, and as you said, it
matches S_IXGRP.
- related to that "I don't understand the semantics", the
"documentation" for that thing doesn't make sense either:
+ The
+ main usage is for script
+ interpreters to enforce a policy
+ consistent with the kernel's one
+ (through sysctl configuration or LSM
+ policy). */
I'll synchronize the documentation with a next series.
Now, what I *think* you mean is
See a following email in reply to Kees.
[...]
And yes, we still need to talk details:
- no backwards compatibility issues, because we've happily always
checked 'mode' for being valid, so old kernels will always return
-EINVAL.
- POSIX namespace issues for EXECVE_OK means that the name probably
needs some thinking (maybe we just need to call it __ACCESS_OK_EXECVE
internally or something - the kernel actually doesn't even export the
existing [FRWX]_OK values, because we "know" they map tho the usual
"owner RWX" bits, with F being "no bit set")
Right, I cannot find a better name for now.
See a following email in reply to Kees.
[...]
So to recap: I'm very much ok with some access() extension, but I
think even that very much needs clarification, and the existing patch
is just odd in many many ways.
This v8 was kind of an early version, I'll update everything. Thanks!
