linux-kernel - [PATCH 4/4] selftests/seccomp: Add test for atomic addfd+send

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Date:   Sat,  1 May 2021 17:18:51 -0700
From:   Sargun Dhillon <sargun@...gun.me>
To:     Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux.dev>,
        Tycho Andersen <tycho@...ho.pizza>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Rodrigo Campos <rodrigo@...volk.io>,
        Mauricio Vásquez Bernal <mauricio@...volk.io>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Mickaël Salaün <mic@...ux.microsoft.com>,
        Sargun Dhillon <sargun@...gun.me>
Subject: [PATCH 4/4] selftests/seccomp: Add test for atomic addfd+send

From: Rodrigo Campos <rodrigo@...volk.io>

This just adds a test to verify that when using the new introduced flag
to ADDFD, a valid fd is added and returned as the syscall result.

Signed-off-by: Rodrigo Campos <rodrigo@...volk.io>
Signed-off-by: Sargun Dhillon <sargun@...gun.me>
---
 tools/testing/selftests/seccomp/seccomp_bpf.c | 38 +++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 98c3b647f54d..e2ba7adc2694 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -235,6 +235,10 @@ struct seccomp_notif_addfd {
 };
 #endif
 
+#ifndef SECCOMP_ADDFD_FLAG_SEND
+#define SECCOMP_ADDFD_FLAG_SEND	(1UL << 1) /* Addfd and return it, atomically */
+#endif
+
 struct seccomp_notif_addfd_small {
 	__u64 id;
 	char weird[4];
@@ -3976,8 +3980,14 @@ TEST(user_notification_addfd)
 	ASSERT_GE(pid, 0);
 
 	if (pid == 0) {
+		/* fds will be added and this value is expected */
 		if (syscall(__NR_getppid) != USER_NOTIF_MAGIC)
 			exit(1);
+
+		/* Atomic addfd+send is received here. Check it is a valid fd */
+		if (fcntl(syscall(__NR_getppid), F_GETFD) == -1)
+			exit(1);
+
 		exit(syscall(__NR_getppid) != USER_NOTIF_MAGIC);
 	}
 
@@ -4056,6 +4066,30 @@ TEST(user_notification_addfd)
 	ASSERT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
 	ASSERT_EQ(addfd.id, req.id);
 
+	/* Verify we can do an atomic addfd and send */
+	addfd.newfd = 0;
+	addfd.flags = SECCOMP_ADDFD_FLAG_SEND;
+	fd = ioctl(listener, SECCOMP_IOCTL_NOTIF_ADDFD, &addfd);
+
+	/* Child has fds 0-6 and 42 used, we expect the lower fd available: 7 */
+	EXPECT_EQ(fd, 7);
+	EXPECT_EQ(filecmp(getpid(), pid, memfd, fd), 0);
+
+	/*
+	 * This sets the ID of the ADD FD to the last request plus 1. The
+	 * notification ID increments 1 per notification.
+	 */
+	addfd.id = req.id + 1;
+
+	/* This spins until the underlying notification is generated */
+	while (ioctl(listener, SECCOMP_IOCTL_NOTIF_ADDFD, &addfd) != -1 &&
+	       errno != -EINPROGRESS)
+		nanosleep(&delay, NULL);
+
+	memset(&req, 0, sizeof(req));
+	ASSERT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
+	ASSERT_EQ(addfd.id, req.id);
+
 	resp.id = req.id;
 	resp.error = 0;
 	resp.val = USER_NOTIF_MAGIC;
@@ -4116,6 +4150,10 @@ TEST(user_notification_addfd_rlimit)
 	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_ADDFD, &addfd), -1);
 	EXPECT_EQ(errno, EMFILE);
 
+	addfd.flags = SECCOMP_ADDFD_FLAG_SEND;
+	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_ADDFD, &addfd), -1);
+	EXPECT_EQ(errno, EMFILE);
+
 	addfd.newfd = 100;
 	addfd.flags = SECCOMP_ADDFD_FLAG_SETFD;
 	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_ADDFD, &addfd), -1);
-- 
2.25.1