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Commit 8589b4e0 authored by David Howells's avatar David Howells Committed by Linus Torvalds
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[PATCH] Keys: Use RCU to manage session keyring pointer 



The attached patch uses RCU to manage the session keyring pointer in struct
signal_struct.  This means that searching need not disable interrupts and get
a the sighand spinlock to access this pointer.  Furthermore, by judicious use
of rcu_read_(un)lock(), this patch also avoids the need to take and put
refcounts on the session keyring itself, thus saving on even more atomic ops.

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 7888e7ff

security/keys/process_keys.c

+21 −21
Original line number Diff line number Diff line 
/* process_keys.c: management of a process's keyrings

 *

 * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.

 * Copyright (C) 2004-5 Red Hat, Inc. All Rights Reserved.

 * Written by David Howells (dhowells@redhat.com)

 *

 * This program is free software; you can redistribute it and/or
@@ -181,7 +181,7 @@ static int install_process_keyring(struct task_struct *tsk) 
			goto error;

		}



		/* attach or swap keyrings */

		/* attach keyring */

		spin_lock_irqsave(&tsk->sighand->siglock, flags);

		if (!tsk->signal->process_keyring) {

			tsk->signal->process_keyring = keyring;
@@ -227,12 +227,14 @@ static int install_session_keyring(struct task_struct *tsk, 


	/* install the keyring */

	spin_lock_irqsave(&tsk->sighand->siglock, flags);

	old = tsk->signal->session_keyring;

	tsk->signal->session_keyring = keyring;

	old = rcu_dereference(tsk->signal->session_keyring);

	rcu_assign_pointer(tsk->signal->session_keyring, keyring);

	spin_unlock_irqrestore(&tsk->sighand->siglock, flags);



	ret = 0;



	/* we're using RCU on the pointer */

	synchronize_kernel();

	key_put(old);

 error:

	return ret;
@@ -245,8 +247,6 @@ static int install_session_keyring(struct task_struct *tsk, 
 */

int copy_thread_group_keys(struct task_struct *tsk)

{

	unsigned long flags;



	key_check(current->thread_group->session_keyring);

	key_check(current->thread_group->process_keyring);
@@ -254,10 +254,10 @@ int copy_thread_group_keys(struct task_struct *tsk) 
	tsk->signal->process_keyring = NULL;



	/* same session keyring */

	spin_lock_irqsave(&current->sighand->siglock, flags);

	rcu_read_lock();

	tsk->signal->session_keyring =

		key_get(current->signal->session_keyring);

	spin_unlock_irqrestore(&current->sighand->siglock, flags);

		key_get(rcu_dereference(current->signal->session_keyring));

	rcu_read_unlock();



	return 0;
@@ -381,8 +381,7 @@ struct key *search_process_keyrings_aux(struct key_type *type, 
					key_match_func_t match)

{

	struct task_struct *tsk = current;

	unsigned long flags;

	struct key *key, *ret, *err, *tmp;

	struct key *key, *ret, *err;



	/* we want to return -EAGAIN or -ENOKEY if any of the keyrings were

	 * searchable, but we failed to find a key or we found a negative key;
@@ -436,17 +435,18 @@ struct key *search_process_keyrings_aux(struct key_type *type, 
	}



	/* search the session keyring last */

	spin_lock_irqsave(&tsk->sighand->siglock, flags);



	tmp = tsk->signal->session_keyring;

	if (!tmp)

		tmp = tsk->user->session_keyring;

	atomic_inc(&tmp->usage);



	spin_unlock_irqrestore(&tsk->sighand->siglock, flags);

	if (tsk->signal->session_keyring) {

		rcu_read_lock();

		key = keyring_search_aux(

			rcu_dereference(tsk->signal->session_keyring),

			type, description, match);

		rcu_read_unlock();

	}

	else {

		key = keyring_search_aux(tsk->user->session_keyring,

					 type, description, match);

	}



	key = keyring_search_aux(tmp, type, description, match);

	key_put(tmp);

	if (!IS_ERR(key))

		goto found;

security/keys/request_key.c

+3 −4
Original line number Diff line number Diff line
@@ -175,13 +175,12 @@ static struct key *__request_key_construction(struct key_type *type, 
	key->expiry = now.tv_sec + key_negative_timeout;



	if (current->signal->session_keyring) {

		unsigned long flags;

		struct key *keyring;



		spin_lock_irqsave(&current->sighand->siglock, flags);

		keyring = current->signal->session_keyring;

		rcu_read_lock();

		keyring = rcu_dereference(current->signal->session_keyring);

		atomic_inc(&keyring->usage);

		spin_unlock_irqrestore(&current->sighand->siglock, flags);

		rcu_read_unlock();



		key_link(keyring, key);

		key_put(keyring);