[PATCH] Keys: Improve usage of memory barriers and remove IRQ disablement

Remove an unnecessary memory barrier (implicit in rcu_dereference()) from
install_session_keyring().

install_session_keyring() is also rearranged a little to make it slightly
more efficient.

As install_*_keyring() may schedule (in synchronize_rcu() or
keyring_alloc()), they may not be entered with interrupts disabled - and so
there's no point saving the interrupt disablement state over the critical
section.

exec_keys() will also be invoked with interrupts enabled, and so that doesn't
need to save the interrupt state either.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 20 insertions, 21 deletions

diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index f6940618e345..217a0bef3c82 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -168,11 +168,12 @@ error:
  */
 int install_process_keyring(struct task_struct *tsk)
 {
-        unsigned long flags;
         struct key *keyring;
         char buf[20];
         int ret;
 
+        might_sleep();
+
         if (!tsk->signal->process_keyring) {
                 sprintf(buf, "_pid.%u", tsk->tgid);
 
@@ -183,12 +184,12 @@ int install_process_keyring(struct task_struct *tsk)
                 }
 
                 /* attach keyring */
-                spin_lock_irqsave(&tsk->sighand->siglock, flags);
+                spin_lock_irq(&tsk->sighand->siglock);
                 if (!tsk->signal->process_keyring) {
                         tsk->signal->process_keyring = keyring;
                         keyring = NULL;
                 }
-                spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
+                spin_unlock_irq(&tsk->sighand->siglock);
 
                 key_put(keyring);
         }
@@ -207,38 +208,37 @@ error:
 static int install_session_keyring(struct task_struct *tsk,
                                    struct key *keyring)
 {
-        unsigned long flags;
         struct key *old;
         char buf[20];
-        int ret;
+
+        might_sleep();
 
         /* create an empty session keyring */
         if (!keyring) {
                 sprintf(buf, "_ses.%u", tsk->tgid);
 
                 keyring = keyring_alloc(buf, tsk->uid, tsk->gid, 1, NULL);
-                if (IS_ERR(keyring)) {
-                        ret = PTR_ERR(keyring);
-                        goto error;
-                }
+                if (IS_ERR(keyring))
+                        return PTR_ERR(keyring);
         }
         else {
                 atomic_inc(&keyring->usage);
         }
 
         /* install the keyring */
-        spin_lock_irqsave(&tsk->sighand->siglock, flags);
-        old = rcu_dereference(tsk->signal->session_keyring);
+        spin_lock_irq(&tsk->sighand->siglock);
+        old = tsk->signal->session_keyring;
         rcu_assign_pointer(tsk->signal->session_keyring, keyring);
-        spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
+        spin_unlock_irq(&tsk->sighand->siglock);
 
-        ret = 0;
+        /* we're using RCU on the pointer, but there's no point synchronising
+         * on it if it didn't previously point to anything */
+        if (old) {
+                synchronize_rcu();
+                key_put(old);
+        }
 
-        /* we're using RCU on the pointer */
-        synchronize_rcu();
-        key_put(old);
-error:
-        return ret;
+        return 0;
 
 } /* end install_session_keyring() */
 
@@ -311,7 +311,6 @@ void exit_keys(struct task_struct *tsk)
  */
 int exec_keys(struct task_struct *tsk)
 {
-        unsigned long flags;
         struct key *old;
 
         /* newly exec'd tasks don't get a thread keyring */
@@ -323,10 +322,10 @@ int exec_keys(struct task_struct *tsk)
         key_put(old);
 
         /* discard the process keyring from a newly exec'd task */
-        spin_lock_irqsave(&tsk->sighand->siglock, flags);
+        spin_lock_irq(&tsk->sighand->siglock);
         old = tsk->signal->process_keyring;
         tsk->signal->process_keyring = NULL;
-        spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
+        spin_unlock_irq(&tsk->sighand->siglock);
 
         key_put(old);