linux-kernel - [PATCH 1/3] seccomp: interrupt SECCOMP_IOCTL_NOTIF

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Date: Thu, 23 May 2024 01:45:38 +0000
From: Andrei Vagin <avagin@...gle.com>
To: Kees Cook <keescook@...omium.org>, Andy Lutomirski <luto@...capital.net>, 
	Will Drewry <wad@...omium.org>, Oleg Nesterov <oleg@...hat.com>, 
	Christian Brauner <brauner@...nel.org>
Cc: linux-kernel@...r.kernel.org, Tycho Andersen <tandersen@...flix.com>, 
	Andrei Vagin <avagin@...gle.com>, Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 1/3] seccomp: interrupt SECCOMP_IOCTL_NOTIF_RECV when all
 users have exited

SECCOMP_IOCTL_NOTIF_RECV promptly returns when a seccomp filter becomes
unused, as a filter without users can't trigger any events.

Previously, event listeners had to rely on epoll to detect when all
processes had exited.

The change is based on the 'commit 99cdb8b9a573 ("seccomp: notify about
unused filter")' which implemented (E)POLLHUP notifications.

Reviewed-by: Christian Brauner <brauner@...nel.org>
Signed-off-by: Andrei Vagin <avagin@...gle.com>
---
 kernel/seccomp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index f70e031e06a8..35435e8f1035 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -1466,7 +1466,7 @@ static int recv_wake_function(wait_queue_entry_t *wait, unsigned int mode, int s
 				  void *key)
 {
 	/* Avoid a wakeup if event not interesting for us. */
-	if (key && !(key_to_poll(key) & (EPOLLIN | EPOLLERR)))
+	if (key && !(key_to_poll(key) & (EPOLLIN | EPOLLERR | EPOLLHUP)))
 		return 0;
 	return autoremove_wake_function(wait, mode, sync, key);
 }
@@ -1476,6 +1476,9 @@ static int recv_wait_event(struct seccomp_filter *filter)
 	DEFINE_WAIT_FUNC(wait, recv_wake_function);
 	int ret;
 
+	if (refcount_read(&filter->users) == 0)
+		return 0;
+
 	if (atomic_dec_if_positive(&filter->notif->requests) >= 0)
 		return 0;
 
@@ -1484,6 +1487,8 @@ static int recv_wait_event(struct seccomp_filter *filter)
 
 		if (atomic_dec_if_positive(&filter->notif->requests) >= 0)
 			break;
+		if (refcount_read(&filter->users) == 0)
+			break;
 
 		if (ret)
 			return ret;
-- 
2.45.1.288.g0e0cd299f1-goog