Commit 1a26feb9 authored by David Howells's avatar David Howells Committed by Linus Torvalds
Browse files

[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: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 25a80759

security/keys/process_keys.c

+20 −21
Original line number Diff line number Diff line
@@ -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 */

	/* 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);

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);

CRA Git | Maintained and supported by SUSTech CRA and CCSE