audit: Call tty_audit_push_task() outside preempt disabled
While auditing all tasklist_lock read_lock sites I stumbled over the
following call chain:
audit_prepare_user_tty()
read_lock(&tasklist_lock);
tty_audit_push_task();
mutex_lock(&buf->mutex);
--> buf->mutex is locked with preemption disabled.
Solve this by acquiring a reference to the task struct under
rcu_read_lock and call tty_audit_push_task outside of the preempt
disabled region.
Move all code which needs to be protected by sighand lock into
tty_audit_push_task() and use lock/unlock_sighand as we do not hold
tasklist_lock.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/kernel/audit.c b/kernel/audit.c
index a300931..8429afe 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -467,23 +467,16 @@
struct task_struct *tsk;
int err;
- read_lock(&tasklist_lock);
+ rcu_read_lock();
tsk = find_task_by_vpid(pid);
- err = -ESRCH;
- if (!tsk)
- goto out;
- err = 0;
-
- spin_lock_irq(&tsk->sighand->siglock);
- if (!tsk->signal->audit_tty)
- err = -EPERM;
- spin_unlock_irq(&tsk->sighand->siglock);
- if (err)
- goto out;
-
- tty_audit_push_task(tsk, loginuid, sessionid);
-out:
- read_unlock(&tasklist_lock);
+ if (!tsk) {
+ rcu_read_unlock();
+ return -ESRCH;
+ }
+ get_task_struct(tsk);
+ rcu_read_unlock();
+ err = tty_audit_push_task(tsk, loginuid, sessionid);
+ put_task_struct(tsk);
return err;
}