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seccomp: don't use semaphore and wait_queue together 

The main reason is to use new wake_up helpers that will be added in the
following patches. But here are a few other reasons:

* if we use two different ways, we always need to call them both. This
  patch fixes seccomp_notify_recv where we forgot to call wake_up_poll
  in the error path.

* If we use one primitive, we can control how many waiters are woken up
  for each request. Our goal is to wake up just one that will handle a
  request. Right now, wake_up_poll can wake up one waiter and
  up(&match->notif->request) can wake up one more.

Signed-off-by: Andrei Vagin <avagin@google.com>
Acked-by: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230308073201.3102738-2-avagin@google.com
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Andrei Vagin 2023-03-07 23:31:56 -08:00 committed by Kees Cook
parent fdf0eaf114
commit 4943b66df1
1 changed files with 36 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
kernel/seccomp.c
View File

@ -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_inc(&match->notif->requests);
wake_up_poll(&match->wqh, EPOLLIN | EPOLLRDNORM);
/*
@ -1450,6 +1450,37 @@ find_notification(struct seccomp_filter *filter, u64 id)
return NULL;
}
static int recv_wake_function(wait_queue_entry_t *wait, unsigned int mode, int sync,
void *key)
{
/* Avoid a wakeup if event not interesting for us. */
if (key && !(key_to_poll(key) & (EPOLLIN | EPOLLERR)))
return 0;
return autoremove_wake_function(wait, mode, sync, key);
}
static int recv_wait_event(struct seccomp_filter *filter)
{
DEFINE_WAIT_FUNC(wait, recv_wake_function);
int ret;
if (atomic_dec_if_positive(&filter->notif->requests) >= 0)
return 0;
for (;;) {
ret = prepare_to_wait_event(&filter->wqh, &wait, TASK_INTERRUPTIBLE);
if (atomic_dec_if_positive(&filter->notif->requests) >= 0)
break;
if (ret)
return ret;
schedule();
}
finish_wait(&filter->wqh, &wait);
return 0;
}
static long seccomp_notify_recv(struct seccomp_filter *filter,
void __user *buf)
@ -1467,7 +1498,7 @@ static long seccomp_notify_recv(struct seccomp_filter *filter,
memset(&unotif, 0, sizeof(unotif));
ret = down_interruptible(&filter->notif->request);
ret = recv_wait_event(filter);
if (ret < 0)
return ret;
@ -1515,7 +1546,8 @@ out:
if (should_sleep_killable(filter, knotif))
complete(&knotif->ready);
knotif->state = SECCOMP_NOTIFY_INIT;
up(&filter->notif->request);
atomic_inc(&filter->notif->requests);
wake_up_poll(&filter->wqh, EPOLLIN | EPOLLRDNORM);
}
mutex_unlock(&filter->notify_lock);
}
@ -1777,7 +1809,6 @@ static struct file *init_listener(struct seccomp_filter *filter)
if (!filter->notif)
goto out;
sema_init(&filter->notif->request, 0);
filter->notif->next_id = get_random_u64();
INIT_LIST_HEAD(&filter->notif->notifications);