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Subject[PATCH] Keys: Improve usage of memory barriers and remove IRQ disablement
Date
The attached patch adds a missing memory barrier into the key_put() and removes
an unnecessary barrier 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.
---
security/keys/key.c | 1 +
security/keys/process_keys.c | 41 ++++++++++++++++++++---------------------
2 files changed, 21 insertions(+), 21 deletions(-)
diff --git a/security/keys/key.c b/security/keys/key.c
index 99781b7..d8a6e00 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -619,6 +619,7 @@ void key_put(struct key *key)
if (key) {
key_check(key);

+ smp_mb__before_atomic_dec();
if (atomic_dec_and_test(&key->usage))
schedule_work(&key_cleanup_task);
}
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index 74cb79e..ad123c3 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -167,11 +167,12 @@ 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);

@@ -182,12 +183,12 @@ int install_process_keyring(struct task_
}

/* 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);
}
@@ -206,38 +207,37 @@ 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() */

@@ -310,7 +310,6 @@ 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 */
@@ -322,10 +321,10 @@ 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);

-
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