On Fri, Dec 02, 2016 at 10:57:42AM +0100, Miklos Szeredi wrote:

On Tue, Oct 11, 2016 at 2:50 PM, Andreas Gruenbacher
[off-list ref] wrote:

quoted

Normally, deleting a file requires MAY_WRITE access to the parent
directory.  With richacls, a file may be deleted with MAY_DELETE_CHILD access
to the parent directory or with MAY_DELETE_SELF access to the file.

To support that, pass the MAY_DELETE_CHILD mask flag to inode_permission()
when checking for delete access inside a directory, and MAY_DELETE_SELF
when checking for delete access to a file itself.

The MAY_DELETE_SELF permission overrides the sticky directory check.

And MAY_DELETE_SELF seems totally inappropriate to any kind of rename,
since from the point of view of the inode we are not doing anything at
all.  The modifications are all in the parent(s), and that's where the
permission checks need to be.

I'm having a hard time finding an authoritative reference here (Samba
people might be able to help), but my understanding is that Windows
gives this a meaning something like "may I delete a link to this file".

(And not even "may I delete the *last* link to this file", which might
also sound more logical.)

--b.

quoted

@@ -2780,14 +2780,20 @@ static int may_delete_or_replace(struct inode *dir, struct dentry *victim,
        BUG_ON(victim->d_parent->d_inode != dir);
        audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE);

-       error = inode_permission(dir, mask);
+       error = inode_permission(dir, mask | MAY_WRITE | MAY_DELETE_CHILD);
+       if (!error && check_sticky(dir, inode))
+               error = -EPERM;
+       if (error && IS_RICHACL(inode) &&
+           inode_permission(inode, MAY_DELETE_SELF) == 0 &&
+           inode_permission(dir, mask) == 0)
+               error = 0;

Why is MAY_WRITE missing here?  Everything not aware of
MAY_DELETE_SELF (e.g. LSMs) will still need MAY_WRITE otherwise this
is going to be a loophole.

Thanks,
Miklos
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