linux-kernel - [PATCH] selftests/seccomp: More closely track fds being assigned

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Message-Id: <20210527032948.3730953-1-keescook@chromium.org>
Date:   Wed, 26 May 2021 20:29:48 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Sargun Dhillon <sargun@...gun.me>, containers@...ts.linux.dev,
        Tycho Andersen <tycho@...ho.pizza>,
        "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>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>
Subject: [PATCH] selftests/seccomp: More closely track fds being assigned

Since the open fds might not always start at "4" (especially when
running under kselftest, etc), start counting from the first assigned
fd, rather than using the more permissive EXPECT_GE(fd, 0).

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 tools/testing/selftests/seccomp/seccomp_bpf.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index e2ba7adc2694..03b37e660965 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -3954,7 +3954,7 @@ TEST(user_notification_addfd)
 {
 	pid_t pid;
 	long ret;
-	int status, listener, memfd, fd;
+	int status, listener, memfd, fd, nextfd;
 	struct seccomp_notif_addfd addfd = {};
 	struct seccomp_notif_addfd_small small = {};
 	struct seccomp_notif_addfd_big big = {};
@@ -3963,18 +3963,21 @@ TEST(user_notification_addfd)
 	/* 100 ms */
 	struct timespec delay = { .tv_nsec = 100000000 };
 
+	/* There may be arbitrary already-open fds at test start. */
 	memfd = memfd_create("test", 0);
 	ASSERT_GE(memfd, 0);
+	nextfd = memfd + 1;
 
 	ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
 	ASSERT_EQ(0, ret) {
 		TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!");
 	}
 
+	/* fd: 4 */
 	/* Check that the basic notification machinery works */
 	listener = user_notif_syscall(__NR_getppid,
 				      SECCOMP_FILTER_FLAG_NEW_LISTENER);
-	ASSERT_GE(listener, 0);
+	ASSERT_EQ(listener, nextfd++);
 
 	pid = fork();
 	ASSERT_GE(pid, 0);
@@ -4029,14 +4032,14 @@ TEST(user_notification_addfd)
 
 	/* Verify we can set an arbitrary remote fd */
 	fd = ioctl(listener, SECCOMP_IOCTL_NOTIF_ADDFD, &addfd);
-	EXPECT_GE(fd, 0);
+	EXPECT_EQ(fd, nextfd++);
 	EXPECT_EQ(filecmp(getpid(), pid, memfd, fd), 0);
 
 	/* Verify we can set an arbitrary remote fd with large size */
 	memset(&big, 0x0, sizeof(big));
 	big.addfd = addfd;
 	fd = ioctl(listener, SECCOMP_IOCTL_NOTIF_ADDFD_BIG, &big);
-	EXPECT_GE(fd, 0);
+	EXPECT_EQ(fd, nextfd++);
 
 	/* Verify we can set a specific remote fd */
 	addfd.newfd = 42;
@@ -4070,9 +4073,11 @@ TEST(user_notification_addfd)
 	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);
+	/*
+	 * Child has earlier "low" fds and now 42, so we expect the next
+	 * lowest available fd to be assigned here.
+	 */
+	EXPECT_EQ(fd, nextfd++);
 	EXPECT_EQ(filecmp(getpid(), pid, memfd, fd), 0);
 
 	/*
-- 
2.25.1