Re: [PATCH v3] add group restriction bitmap

Oleg Nesterov
2024-10-01T15:04:24Z

We can't understand each other. I guess I missed something...

On 10/01, stsp wrote:
>
> 01.10.2024 16:02, Oleg Nesterov пишет:
> >On 10/01, stsp wrote:
> >>01.10.2024 14:15, Oleg Nesterov пишет:
> >>>Suppose we change groups_search()
> >>>
> >>> --- a/kernel/groups.c
> >>> +++ b/kernel/groups.c
> >>> @@ -104,8 +104,11 @@ int groups_search(const struct group_info *group_info, kgid_t grp)
> >>> left = mid + 1;
> >>> else if (gid_lt(grp, group_info->gid[mid]))
> >>> right = mid;
> >>> - else
> >>> - return 1;
> >>> + else {
> >>> + bool r = mid < BITS_PER_LONG &&
> >>> + test_bit(mid, &group_info->restrict_bitmap);
> >>> + return r ? -1 : 1;
> >>> + }
> >>> }
> >>> return 0;
> >>> }
> >>>
> >>>so that it returns, say, -1 if the found grp is restricted.
> >>>
> >>>Then everything else can be greatly simplified, afaics...
> >>This will mean updating all callers
> >>of groups_search(), in_group_p(),
> >>in_egroup_p(), vfsxx_in_group_p()
> >Why? I think with this change you do not need to touch in_group_p/etc at all.
> >
> >>if in_group_p() returns -1 for not found
> >>and 0 for gid,
> >With the the change above in_group_p() returns 0 if not found, !0 otherwise.
> >It returns -1 if grp != cred->fsgid and the found grp is restricted.
>
> in_group_p() doesn't check if the
> group is restricted or not.

And it shouldn't. It returns the result of groups_search() if this
grp is supplementary or "not found".

> acl_permission_check() does, but
> in your example it doesn't as well.

But it does??? see below...

> I think you mean to move the
> restrict_bitmap check upwards to
> in_group_p()?

No, I meant to move the restrict_bitmap check to groups_search(), see the patch
above.

> Anyway, suppose you don't mean that.
> In this case:
> 1. in_group_p() and in_egroup_p()
>   should be changed:
> -  int retval = 1;
> + int retval = -1;

Why? -1 means that the grp is supplementary and restricted.

> There are also the callers of groups_search()
> in kernel/auditsc.c and they should
> be updated.

Why? I don't think so. audit_filter_rules() uses the result of groups_search()
as a boolean.

> >So acl_permission_check() can simply do
> >
> > if (mask & (mode ^ (mode >> 3))) {
> > vfsgid_t vfsgid = i_gid_into_vfsgid(idmap, inode);
> > int xxx = vfsgid_in_group_p(vfsgid);
> >
> > if (xxx) {
> > if (mask & ~(mode >> 3))
> > return -EACCES;
> > if (xxx > 0)
> > return 0;
> > /* If we hit restrict_bitmap, then check Others. */
> > }
> > }
>
> Well, in my impl it should check
> the bitmap right here, but you removed
> that.

No, I didn't remove the check, this code relies on the change in
groups_search(). Note the "xxx > 0" check.

I must have missed something :/

Oleg.