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authorAndrei Vagin <avagin@google.com>2023-03-07 23:31:56 -0800
committerKees Cook <keescook@chromium.org>2023-07-17 16:08:08 -0700
commit4943b66df18a0e8aedd006792ed73257cd2da8f8 (patch)
treee6b3132439cb92e619d1c3a360bcb2e9011fc2c7
parentfdf0eaf11452d72945af31804e2a1048ee1b574c (diff)
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>
-rw-r--r--kernel/seccomp.c41
1 files changed, 36 insertions, 5 deletions
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index d3e584065c7f..1386dcedda1a 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_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);