audit: Use rcu for task lookup protection

Protect the task lookups in audit_receive_msg() with rcu_read_lock()
instead of tasklist_lock and use lock/unlock_sighand to protect
against the exit race.

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>

1 files changed, 14 insertions, 16 deletions

diff --git a/kernel/audit.c b/kernel/audit.c
index 57f4038694d1..77770a034d59 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -873,17 +873,16 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
         case AUDIT_TTY_GET: {
                 struct audit_tty_status s;
                 struct task_struct *tsk;
+                unsigned long flags;
 
-                read_lock(&tasklist_lock);
+                rcu_read_lock();
                 tsk = find_task_by_vpid(pid);
-                if (!tsk)
-                        err = -ESRCH;
-                else {
-                        spin_lock_irq(&tsk->sighand->siglock);
+                if (tsk && lock_task_sighand(tsk, &flags)) {
                         s.enabled = tsk->signal->audit_tty != 0;
-                        spin_unlock_irq(&tsk->sighand->siglock);
-                }
-                read_unlock(&tasklist_lock);
+                        unlock_task_sighand(tsk, &flags);
+                } else
+                        err = -ESRCH;
+                rcu_read_unlock();
 
                 if (!err)
                         audit_send_reply(NETLINK_CB(skb).pid, seq,
@@ -893,22 +892,21 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
         case AUDIT_TTY_SET: {
                 struct audit_tty_status *s;
                 struct task_struct *tsk;
+                unsigned long flags;
 
                 if (nlh->nlmsg_len < sizeof(struct audit_tty_status))
                         return -EINVAL;
                 s = data;
                 if (s->enabled != 0 && s->enabled != 1)
                         return -EINVAL;
-                read_lock(&tasklist_lock);
+                rcu_read_lock();
                 tsk = find_task_by_vpid(pid);
-                if (!tsk)
-                        err = -ESRCH;
-                else {
-                        spin_lock_irq(&tsk->sighand->siglock);
+                if (tsk && lock_task_sighand(tsk, &flags)) {
                         tsk->signal->audit_tty = s->enabled != 0;
-                        spin_unlock_irq(&tsk->sighand->siglock);
-                }
-                read_unlock(&tasklist_lock);
+                        unlock_task_sighand(tsk, &flags);
+                } else
+                        err = -ESRCH;
+                rcu_read_unlock();
                 break;
         }
         default: