On Wed, Jul 18, 2018 at 01:43:40PM +0100, Al Viro wrote:
> It *is* broken. For now leave override_creds() as in your variant, but
> we really want to deal with that crap eventually.
>
> > Okay, so ->open() is a file op, and file ops should use file->f_cred,
> > but how are we going to enforce this?
>
> I'd say we cut down on the use of current_cred() when deep in call chain...
Actually, how about this:
#define call_with_creds(__cred, expr) ({ \
__typeof__(expr) ____res; \
const struct cred *____old = current->cred; \
const struct cred *____new = (__cred); \
rcu_assign_pointer(current->cred, ____new); \
____res = expr; \
BUG_ON(current->cred != ____new); \
rcu_assign_pointer(current->cred, ____old); \
____res; \
})
and replacing
error = open(inode, f);
with
error = call_with_cred(f->f_cred, open(inode, f));
possibly with similar at other methods callsites? Unlike override_creds()
and revert_creds() it's cheap - no validation of creds, no cacheline
ping-pong...
Folks?
