[PATCH 1/3] fork: assign refed credentials earlier
mjguzik at gmail.com
Sat Mar 21 01:57:29 UTC 2015
On Sat, Mar 21, 2015 at 03:51:51AM +0200, Konstantin Belousov wrote:
> On Sat, Mar 21, 2015 at 02:00:38AM +0100, Mateusz Guzik wrote:
> > From: Mateusz Guzik <mjg at freebsd.org>
> > Prior to this change the kernel would take p1's credentials and assign
> > them tempororarily to p2. But p1 could change credentials at that time
> > and in effect give us a use-after-free.
> In which way could it change the credentials ? The assigned credentials
> are taken from td_ucred, which, I thought, are guaranteed to be stable
> for the duration of a syscall.
It takes thread's credential in do_fork. But initial copy is taken
unlocked from struct proc.
Relevant part of the diff:
> > @@ -870,7 +867,7 @@ fork1(struct thread *td, int flags, int pages, struct proc **procp,
> > * XXX: This is ugly; when we copy resource usage, we need to bump
> > * per-cred resource counters.
> > */
> > - proc_set_cred(newproc, p1->p_ucred);
> > + proc_set_cred(newproc, crhold(td->td_ucred));
Mateusz Guzik <mjguzik gmail.com>
More information about the freebsd-current