[PATCH v8 9/9] seccomp: implement SECCOMP_FILTER_FLAG_TSYNC
oleg at redhat.com
Wed Jun 25 11:20:12 PDT 2014
On 06/25, Kees Cook wrote:
> On Wed, Jun 25, 2014 at 10:24 AM, Oleg Nesterov <oleg at redhat.com> wrote:
> > However, do_execve() takes cred_guard_mutex at the start in prepare_bprm_creds()
> > and drops it in install_exec_creds(), so it should solve the problem?
> I can't tell yet. I'm still trying to understand the order of
> operations here. It looks like de_thread() takes the sighand lock.
> do_execve_common does:
> prepare_bprm_creds (takes cred_guard_mutex)
> check_unsafe_exec (checks nnp to set LSM_UNSAFE_NO_NEW_PRIVS)
> prepare_binprm (handles suid escalation, checks nnp separately)
> security_bprm_set_creds (checks LSM_UNSAFE_NO_NEW_PRIVS)
> de_thread (takes and releases sighand->lock)
> install_exec_creds (releases cred_guard_mutex)
Yes, and note that when cred_guard_mutex is dropped all other threads
are already killed,
> I don't see a way to use cred_guard_mutex during tsync (which holds
> sighand->lock) without dead-locking. What were you considering here?
Just take/drop current->signal->cred_guard_mutex along with ->siglock
in seccomp_set_mode_filter() ? Unconditionally on depending on
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