[PATCH v2 3/3] seccomp: test SECCOMP_USER_NOTIF_FLAG_CONTINUE

[Christian Brauner <christian.brauner@xxxxxxxxxx>]

Test whether a syscall can be performed after having been intercepted by
the seccomp notifier. The test uses dup() and kcmp() since it allows us to
nicely test whether the dup() syscall actually succeeded by comparing whether
the fds refer to the same underlying struct file.

Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Will Drewry <wad@xxxxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: Martin KaFai Lau <kafai@xxxxxx>
Cc: Song Liu <songliubraving@xxxxxx>
Cc: Yonghong Song <yhs@xxxxxx>
Cc: Tycho Andersen <tycho@xxxxxxxx>
CC: Tyler Hicks <tyhicks@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: linux-kselftest@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Cc: bpf@xxxxxxxxxxxxxxx
---
/* v2 */
- Shuah Khan <shuah@xxxxxxxxxx>:
  - skip test on missing precondition

/* v1 */
Link: https://lore.kernel.org/r/20190919095903.19370-4-christian.brauner@xxxxxxxxxx
- Christian Brauner <christian.brauner@xxxxxxxxxx>:
  - adapt to new flag name SECCOMP_USER_NOTIF_FLAG_CONTINUE

/* v0 */
Link: https://lore.kernel.org/r/20190918084833.9369-5-christian.brauner@xxxxxxxxxx
---
 tools/testing/selftests/seccomp/seccomp_bpf.c | 107 ++++++++++++++++++
 1 file changed, 107 insertions(+)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index e996d7b7fd6e..2519377ebda3 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -44,6 +44,7 @@
 #include <sys/times.h>
 #include <sys/socket.h>
 #include <sys/ioctl.h>
+#include <linux/kcmp.h>
 
 #include <unistd.h>
 #include <sys/syscall.h>
@@ -167,6 +168,10 @@ struct seccomp_metadata {
 
 #define SECCOMP_RET_USER_NOTIF 0x7fc00000U
 
+#ifndef SECCOMP_USER_NOTIF_FLAG_CONTINUE
+#define SECCOMP_USER_NOTIF_FLAG_CONTINUE 0x00000001
+#endif
+
 #define SECCOMP_IOC_MAGIC		'!'
 #define SECCOMP_IO(nr)			_IO(SECCOMP_IOC_MAGIC, nr)
 #define SECCOMP_IOR(nr, type)		_IOR(SECCOMP_IOC_MAGIC, nr, type)
@@ -3481,6 +3486,108 @@ TEST(seccomp_get_notif_sizes)
 	EXPECT_EQ(sizes.seccomp_notif_resp, sizeof(struct seccomp_notif_resp));
 }
 
+static int filecmp(pid_t pid1, pid_t pid2, int fd1, int fd2)
+{
+#ifdef __NR_kcmp
+	return syscall(__NR_kcmp, pid1, pid2, KCMP_FILE, fd1, fd2);
+#else
+	errno = ENOSYS;
+	return -1;
+#endif
+}
+
+TEST(user_notification_continue)
+{
+	pid_t pid;
+	long ret;
+	int status, listener;
+	struct seccomp_notif req = {};
+	struct seccomp_notif_resp resp = {};
+	struct pollfd pollfd;
+
+	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!");
+	}
+
+	listener = user_trap_syscall(__NR_dup, SECCOMP_FILTER_FLAG_NEW_LISTENER);
+	ASSERT_GE(listener, 0);
+
+	pid = fork();
+	ASSERT_GE(pid, 0);
+
+	if (pid == 0) {
+		int dup_fd, pipe_fds[2];
+		pid_t self;
+
+		ret = pipe(pipe_fds);
+		if (ret < 0)
+			exit(1);
+
+		dup_fd = dup(pipe_fds[0]);
+		if (dup_fd < 0)
+			exit(1);
+
+		self = getpid();
+
+		ret = filecmp(self, self, pipe_fds[0], dup_fd);
+		if (ret)
+			exit(2);
+
+		exit(0);
+	}
+
+	pollfd.fd = listener;
+	pollfd.events = POLLIN | POLLOUT;
+
+	EXPECT_GT(poll(&pollfd, 1, -1), 0);
+	EXPECT_EQ(pollfd.revents, POLLIN);
+
+	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
+
+	pollfd.fd = listener;
+	pollfd.events = POLLIN | POLLOUT;
+
+	EXPECT_GT(poll(&pollfd, 1, -1), 0);
+	EXPECT_EQ(pollfd.revents, POLLOUT);
+
+	EXPECT_EQ(req.data.nr, __NR_dup);
+
+	resp.id = req.id;
+	resp.flags = SECCOMP_USER_NOTIF_FLAG_CONTINUE;
+
+	/*
+	 * Verify that setting SECCOMP_USER_NOTIF_FLAG_CONTINUE enforces other
+	 * args be set to 0.
+	 */
+	resp.error = 0;
+	resp.val = USER_NOTIF_MAGIC;
+	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), -1);
+	EXPECT_EQ(errno, EINVAL);
+
+	resp.error = USER_NOTIF_MAGIC;
+	resp.val = 0;
+	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), -1);
+	EXPECT_EQ(errno, EINVAL);
+
+	resp.error = 0;
+	resp.val = 0;
+	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), 0) {
+		if (errno == EINVAL)
+			XFAIL(goto skip, "Kernel does not support SECCOMP_USER_NOTIF_FLAG_CONTINUE");
+	}
+
+skip:
+	EXPECT_EQ(waitpid(pid, &status, 0), pid);
+	EXPECT_EQ(true, WIFEXITED(status));
+	EXPECT_EQ(0, WEXITSTATUS(status)) {
+		if (WEXITSTATUS(status) == 2) {
+			XFAIL(return, "Kernel does not support kcmp() syscall");
+			return;
+		}
+	}
+}
+
 /*
  * TODO:
  * - add microbenchmarks
-- 
2.23.0