[PATCH 1/4] seccomp: don't use semaphore and wait_queue together

Andrei Vagin
2022-08-30T01:44:18Z

Here is no reason to use two different primitives that do similar things.

Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
kernel/seccomp.c | 38 ++++++++++++++++++++++++++------------
1 file changed, 26 insertions(+), 12 deletions(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index e9852d1b4a5e..667fd2d89464 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -145,7 +145,7 @@ struct seccomp_kaddfd {
* @notifications: A list of struct seccomp_knotif elements.
*/
struct notification {
- struct semaphore request;
+ atomic_t requests;
u64 next_id;
struct list_head notifications;
};
@@ -1116,7 +1116,7 @@ static int seccomp_do_user_notification(int this_syscall,
list_add_tail(&n.list, &match->notif->notifications);
INIT_LIST_HEAD(&n.addfd);

- up(&match->notif->request);
+ atomic_add(1, &match->notif->requests);
wake_up_poll(&match->wqh, EPOLLIN | EPOLLRDNORM);

/*
@@ -1388,8 +1388,10 @@ static long seccomp_set_mode_strict(void)
#ifdef CONFIG_SECCOMP_FILTER
static void seccomp_notify_free(struct seccomp_filter *filter)
{
- kfree(filter->notif);
- filter->notif = NULL;
+ struct notification *notif = filter->notif;
+
+ WRITE_ONCE(filter->notif, NULL);
+ kfree_rcu(notif);
}

static void seccomp_notify_detach(struct seccomp_filter *filter)
@@ -1450,6 +1452,16 @@ find_notification(struct seccomp_filter *filter, u64 id)
return NULL;
}

+static bool notify_wakeup(struct seccomp_filter *filter)
+{
+ bool ret;
+
+ rcu_read_lock();
+ ret = atomic_add_unless(&filter->notif->requests, -1, 0);
+ rcu_read_unlock();
+
+ return ret;
+}

static long seccomp_notify_recv(struct seccomp_filter *filter,
void __user *buf)
@@ -1467,7 +1479,7 @@ static long seccomp_notify_recv(struct seccomp_filter *filter,

memset(&unotif, 0, sizeof(unotif));

- ret = down_interruptible(&filter->notif->request);
+ ret = wait_event_interruptible(filter->wqh, notify_wakeup(filter));
if (ret < 0)
return ret;

@@ -1515,7 +1527,8 @@ static long seccomp_notify_recv(struct seccomp_filter *filter,
if (should_sleep_killable(filter, knotif))
complete(&knotif->ready);
knotif->state = SECCOMP_NOTIFY_INIT;
- up(&filter->notif->request);
+ atomic_add(1, &filter->notif->requests);
+ wake_up_poll(&filter->wqh, EPOLLIN | EPOLLRDNORM);
}
mutex_unlock(&filter->notify_lock);
}
@@ -1771,15 +1784,15 @@ static const struct file_operations seccomp_notify_ops = {
static struct file *init_listener(struct seccomp_filter *filter)
{
struct file *ret;
+ struct notification *notif;

ret = ERR_PTR(-ENOMEM);
- filter->notif = kzalloc(sizeof(*(filter->notif)), GFP_KERNEL);
- if (!filter->notif)
+ notif = kzalloc(sizeof(*notif), GFP_KERNEL);
+ if (!notif)
goto out;

- sema_init(&filter->notif->request, 0);
- filter->notif->next_id = get_random_u64();
- INIT_LIST_HEAD(&filter->notif->notifications);
+ notif->next_id = get_random_u64();
+ INIT_LIST_HEAD(&notif->notifications);

ret = anon_inode_getfile("seccomp notify", &seccomp_notify_ops,
filter, O_RDWR);
@@ -1788,10 +1801,11 @@ static struct file *init_listener(struct seccomp_filter *filter)

/* The file has a reference to it now */
__get_seccomp_filter(filter);
+ WRITE_ONCE(filter->notif, notif);

out_notif:
if (IS_ERR(ret))
- seccomp_notify_free(filter);
+ kfree(notif);
out:
return ret;
}
--
2.37.2