Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  sys: Fix missing rcu protection for __task_cred() access
  signals: Fix more rcu assumptions
  signal: Fix racy access to __task_cred in kill_pid_info_as_uid()

1 files changed, 14 insertions, 11 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 1814e68e4de3..d09692b40376 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -218,13 +218,13 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t flags, int override_rlimi
         struct user_struct *user;
 
         /*
-         * We won't get problems with the target's UID changing under us
-         * because changing it requires RCU be used, and if t != current, the
-         * caller must be holding the RCU readlock (by way of a spinlock) and
-         * we use RCU protection here
+         * Protect access to @t credentials. This can go away when all
+         * callers hold rcu read lock.
          */
+        rcu_read_lock();
         user = get_uid(__task_cred(t)->user);
         atomic_inc(&user->sigpending);
+        rcu_read_unlock();
 
         if (override_rlimit ||
             atomic_read(&user->sigpending) <=
@@ -1179,11 +1179,12 @@ int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
         int ret = -EINVAL;
         struct task_struct *p;
         const struct cred *pcred;
+        unsigned long flags;
 
         if (!valid_signal(sig))
                 return ret;
 
-        read_lock(&tasklist_lock);
+        rcu_read_lock();
         p = pid_task(pid, PIDTYPE_PID);
         if (!p) {
                 ret = -ESRCH;
@@ -1199,14 +1200,16 @@ int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
         ret = security_task_kill(p, info, sig, secid);
         if (ret)
                 goto out_unlock;
-        if (sig && p->sighand) {
-                unsigned long flags;
-                spin_lock_irqsave(&p->sighand->siglock, flags);
-                ret = __send_signal(sig, info, p, 1, 0);
-                spin_unlock_irqrestore(&p->sighand->siglock, flags);
+
+        if (sig) {
+                if (lock_task_sighand(p, &flags)) {
+                        ret = __send_signal(sig, info, p, 1, 0);
+                        unlock_task_sighand(p, &flags);
+                } else
+                        ret = -ESRCH;
         }
 out_unlock:
-        read_unlock(&tasklist_lock);
+        rcu_read_unlock();
         return ret;
 }
 EXPORT_SYMBOL_GPL(kill_pid_info_as_uid);