Merge tag 'threads-v5.8' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

Pull thread updates from Christian Brauner:
 "We have been discussing using pidfds to attach to namespaces for quite
  a while and the patches have in one form or another already existed
  for about a year. But I wanted to wait to see how the general api
  would be received and adopted.

  This contains the changes to make it possible to use pidfds to attach
  to the namespaces of a process, i.e. they can be passed as the first
  argument to the setns() syscall.

  When only a single namespace type is specified the semantics are
  equivalent to passing an nsfd. That means setns(nsfd, CLONE_NEWNET)
  equals setns(pidfd, CLONE_NEWNET).

  However, when a pidfd is passed, multiple namespace flags can be
  specified in the second setns() argument and setns() will attach the
  caller to all the specified namespaces all at once or to none of them.

  Specifying 0 is not valid together with a pidfd. Here are just two
  obvious examples:

    setns(pidfd, CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWNET);
    setns(pidfd, CLONE_NEWUSER);

  Allowing to also attach subsets of namespaces supports various
  use-cases where callers setns to a subset of namespaces to retain
  privilege, perform an action and then re-attach another subset of
  namespaces.

  Apart from significantly reducing the number of syscalls needed to
  attach to all currently supported namespaces (eight "open+setns"
  sequences vs just a single "setns()"), this also allows atomic setns
  to a set of namespaces, i.e. either attaching to all namespaces
  succeeds or we fail without having changed anything.

  This is centered around a new internal struct nsset which holds all
  information necessary for a task to switch to a new set of namespaces
  atomically. Fwiw, with this change a pidfd becomes the only token
  needed to interact with a container. I'm expecting this to be
  picked-up by util-linux for nsenter rather soon.

  Associated with this change is a shiny new test-suite dedicated to
  setns() (for pidfds and nsfds alike)"

* tag 'threads-v5.8' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  selftests/pidfd: add pidfd setns tests
  nsproxy: attach to namespaces via pidfds
  nsproxy: add struct nsset

4 files changed, 482 insertions, 1 deletions

diff --git a/tools/testing/selftests/pidfd/.gitignore b/tools/testing/selftests/pidfd/.gitignore
index 2d4db5afb142..973198a3ec3d 100644
--- a/tools/testing/selftests/pidfd/.gitignore
+++ b/tools/testing/selftests/pidfd/.gitignore
@@ -5,3 +5,4 @@ pidfd_test
 pidfd_wait
 pidfd_fdinfo_test
 pidfd_getfd_test
+pidfd_setns_test
diff --git a/tools/testing/selftests/pidfd/Makefile b/tools/testing/selftests/pidfd/Makefile
index 75a545861375..f4a2f28f926b 100644
--- a/tools/testing/selftests/pidfd/Makefile
+++ b/tools/testing/selftests/pidfd/Makefile
@@ -1,7 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0-only
 CFLAGS += -g -I../../../../usr/include/ -pthread
 
-TEST_GEN_PROGS := pidfd_test pidfd_fdinfo_test pidfd_open_test pidfd_poll_test pidfd_wait pidfd_getfd_test
+TEST_GEN_PROGS := pidfd_test pidfd_fdinfo_test pidfd_open_test \
+	pidfd_poll_test pidfd_wait pidfd_getfd_test pidfd_setns_test
 
 include ../lib.mk
 
diff --git a/tools/testing/selftests/pidfd/config b/tools/testing/selftests/pidfd/config
new file mode 100644
index 000000000000..bb11de90c0c9
--- /dev/null
+++ b/tools/testing/selftests/pidfd/config
@@ -0,0 +1,6 @@
+CONFIG_UTS_NS=y
+CONFIG_IPC_NS=y
+CONFIG_USER_NS=y
+CONFIG_PID_NS=y
+CONFIG_NET_NS=y
+CONFIG_CGROUPS=y
diff --git a/tools/testing/selftests/pidfd/pidfd_setns_test.c b/tools/testing/selftests/pidfd/pidfd_setns_test.c
new file mode 100644
index 000000000000..133ec5b6cda8
--- /dev/null
+++ b/tools/testing/selftests/pidfd/pidfd_setns_test.c
@@ -0,0 +1,473 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <linux/types.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syscall.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <linux/kcmp.h>
+
+#include "pidfd.h"
+#include "../clone3/clone3_selftests.h"
+#include "../kselftest.h"
+#include "../kselftest_harness.h"
+
+enum {
+	PIDFD_NS_USER,
+	PIDFD_NS_MNT,
+	PIDFD_NS_PID,
+	PIDFD_NS_UTS,
+	PIDFD_NS_IPC,
+	PIDFD_NS_NET,
+	PIDFD_NS_CGROUP,
+	PIDFD_NS_PIDCLD,
+	PIDFD_NS_MAX
+};
+
+const struct ns_info {
+	const char *name;
+	int flag;
+} ns_info[] = {
+	[PIDFD_NS_USER]   = { "user",             CLONE_NEWUSER,   },
+	[PIDFD_NS_MNT]    = { "mnt",              CLONE_NEWNS,     },
+	[PIDFD_NS_PID]    = { "pid",              CLONE_NEWPID,    },
+	[PIDFD_NS_UTS]    = { "uts",              CLONE_NEWUTS,    },
+	[PIDFD_NS_IPC]    = { "ipc",              CLONE_NEWIPC,    },
+	[PIDFD_NS_NET]    = { "net",              CLONE_NEWNET,    },
+	[PIDFD_NS_CGROUP] = { "cgroup",           CLONE_NEWCGROUP, },
+	[PIDFD_NS_PIDCLD] = { "pid_for_children", 0,               },
+};
+
+FIXTURE(current_nsset)
+{
+	pid_t pid;
+	int pidfd;
+	int nsfds[PIDFD_NS_MAX];
+
+	pid_t child_pid_exited;
+	int child_pidfd_exited;
+
+	pid_t child_pid1;
+	int child_pidfd1;
+	int child_nsfds1[PIDFD_NS_MAX];
+
+	pid_t child_pid2;
+	int child_pidfd2;
+	int child_nsfds2[PIDFD_NS_MAX];
+};
+
+static int sys_waitid(int which, pid_t pid, int options)
+{
+	return syscall(__NR_waitid, which, pid, NULL, options, NULL);
+}
+
+pid_t create_child(int *pidfd, unsigned flags)
+{
+	struct clone_args args = {
+		.flags		= CLONE_PIDFD | flags,
+		.exit_signal	= SIGCHLD,
+		.pidfd		= ptr_to_u64(pidfd),
+	};
+
+	return sys_clone3(&args, sizeof(struct clone_args));
+}
+
+FIXTURE_SETUP(current_nsset)
+{
+	int i, proc_fd, ret;
+
+	for (i = 0; i < PIDFD_NS_MAX; i++) {
+		self->nsfds[i]		= -EBADF;
+		self->child_nsfds1[i]	= -EBADF;
+		self->child_nsfds2[i]	= -EBADF;
+	}
+
+	proc_fd = open("/proc/self/ns", O_DIRECTORY | O_CLOEXEC);
+	ASSERT_GE(proc_fd, 0) {
+		TH_LOG("%m - Failed to open /proc/self/ns");
+	}
+
+	self->pid = getpid();
+	for (i = 0; i < PIDFD_NS_MAX; i++) {
+		const struct ns_info *info = &ns_info[i];
+		self->nsfds[i] = openat(proc_fd, info->name, O_RDONLY | O_CLOEXEC);
+		if (self->nsfds[i] < 0) {
+			EXPECT_EQ(errno, ENOENT) {
+				TH_LOG("%m - Failed to open %s namespace for process %d",
+				       info->name, self->pid);
+			}
+		}
+	}
+
+	self->pidfd = sys_pidfd_open(self->pid, 0);
+	EXPECT_GT(self->pidfd, 0) {
+		TH_LOG("%m - Failed to open pidfd for process %d", self->pid);
+	}
+
+	/* Create task that exits right away. */
+	self->child_pid_exited = create_child(&self->child_pidfd_exited,
+					      CLONE_NEWUSER | CLONE_NEWNET);
+	EXPECT_GT(self->child_pid_exited, 0);
+
+	if (self->child_pid_exited == 0)
+		_exit(EXIT_SUCCESS);
+
+	ASSERT_EQ(sys_waitid(P_PID, self->child_pid_exited, WEXITED | WNOWAIT), 0);
+
+	self->pidfd = sys_pidfd_open(self->pid, 0);
+	EXPECT_GE(self->pidfd, 0) {
+		TH_LOG("%m - Failed to open pidfd for process %d", self->pid);
+	}
+
+	/* Create tasks that will be stopped. */
+	self->child_pid1 = create_child(&self->child_pidfd1,
+					CLONE_NEWUSER | CLONE_NEWNS |
+					CLONE_NEWCGROUP | CLONE_NEWIPC |
+					CLONE_NEWUTS | CLONE_NEWPID |
+					CLONE_NEWNET);
+	EXPECT_GE(self->child_pid1, 0);
+
+	if (self->child_pid1 == 0) {
+		pause();
+		_exit(EXIT_SUCCESS);
+	}
+
+	self->child_pid2 = create_child(&self->child_pidfd2,
+					CLONE_NEWUSER | CLONE_NEWNS |
+					CLONE_NEWCGROUP | CLONE_NEWIPC |
+					CLONE_NEWUTS | CLONE_NEWPID |
+					CLONE_NEWNET);
+	EXPECT_GE(self->child_pid2, 0);
+
+	if (self->child_pid2 == 0) {
+		pause();
+		_exit(EXIT_SUCCESS);
+	}
+
+	for (i = 0; i < PIDFD_NS_MAX; i++) {
+		char p[100];
+
+		const struct ns_info *info = &ns_info[i];
+
+		self->nsfds[i] = openat(proc_fd, info->name, O_RDONLY | O_CLOEXEC);
+		if (self->nsfds[i] < 0) {
+			EXPECT_EQ(errno, ENOENT) {
+				TH_LOG("%m - Failed to open %s namespace for process %d",
+				       info->name, self->pid);
+			}
+		}
+
+		ret = snprintf(p, sizeof(p), "/proc/%d/ns/%s",
+			       self->child_pid1, info->name);
+		EXPECT_GT(ret, 0);
+		EXPECT_LT(ret, sizeof(p));
+
+		self->child_nsfds1[i] = open(p, O_RDONLY | O_CLOEXEC);
+		if (self->child_nsfds1[i] < 0) {
+			EXPECT_EQ(errno, ENOENT) {
+				TH_LOG("%m - Failed to open %s namespace for process %d",
+				       info->name, self->child_pid1);
+			}
+		}
+
+		ret = snprintf(p, sizeof(p), "/proc/%d/ns/%s",
+			       self->child_pid2, info->name);
+		EXPECT_GT(ret, 0);
+		EXPECT_LT(ret, sizeof(p));
+
+		self->child_nsfds2[i] = open(p, O_RDONLY | O_CLOEXEC);
+		if (self->child_nsfds2[i] < 0) {
+			EXPECT_EQ(errno, ENOENT) {
+				TH_LOG("%m - Failed to open %s namespace for process %d",
+				       info->name, self->child_pid1);
+			}
+		}
+	}
+
+	close(proc_fd);
+}
+
+FIXTURE_TEARDOWN(current_nsset)
+{
+	int i;
+
+	ASSERT_EQ(sys_pidfd_send_signal(self->child_pidfd1,
+					SIGKILL, NULL, 0), 0);
+	ASSERT_EQ(sys_pidfd_send_signal(self->child_pidfd2,
+					SIGKILL, NULL, 0), 0);
+
+	for (i = 0; i < PIDFD_NS_MAX; i++) {
+		if (self->nsfds[i] >= 0)
+			close(self->nsfds[i]);
+		if (self->child_nsfds1[i] >= 0)
+			close(self->child_nsfds1[i]);
+		if (self->child_nsfds2[i] >= 0)
+			close(self->child_nsfds2[i]);
+	}
+
+	if (self->child_pidfd1 >= 0)
+		EXPECT_EQ(0, close(self->child_pidfd1));
+	if (self->child_pidfd2 >= 0)
+		EXPECT_EQ(0, close(self->child_pidfd2));
+	ASSERT_EQ(sys_waitid(P_PID, self->child_pid_exited, WEXITED), 0);
+	ASSERT_EQ(sys_waitid(P_PID, self->child_pid1, WEXITED), 0);
+	ASSERT_EQ(sys_waitid(P_PID, self->child_pid2, WEXITED), 0);
+}
+
+static int preserve_ns(const int pid, const char *ns)
+{
+	int ret;
+	char path[50];
+
+	ret = snprintf(path, sizeof(path), "/proc/%d/ns/%s", pid, ns);
+	if (ret < 0 || (size_t)ret >= sizeof(path))
+		return -EIO;
+
+	return open(path, O_RDONLY | O_CLOEXEC);
+}
+
+static int in_same_namespace(int ns_fd1, pid_t pid2, const char *ns)
+{
+	int ns_fd2 = -EBADF;
+	int ret = -1;
+	struct stat ns_st1, ns_st2;
+
+	ret = fstat(ns_fd1, &ns_st1);
+	if (ret < 0)
+		return -1;
+
+	ns_fd2 = preserve_ns(pid2, ns);
+	if (ns_fd2 < 0)
+		return -1;
+
+	ret = fstat(ns_fd2, &ns_st2);
+	close(ns_fd2);
+	if (ret < 0)
+		return -1;
+
+	/* processes are in the same namespace */
+	if ((ns_st1.st_dev == ns_st2.st_dev) &&
+	    (ns_st1.st_ino == ns_st2.st_ino))
+		return 1;
+
+	/* processes are in different namespaces */
+	return 0;
+}
+
+/* Test that we can't pass garbage to the kernel. */
+TEST_F(current_nsset, invalid_flags)
+{
+	ASSERT_NE(setns(self->pidfd, 0), 0);
+	EXPECT_EQ(errno, EINVAL);
+
+	ASSERT_NE(setns(self->pidfd, -1), 0);
+	EXPECT_EQ(errno, EINVAL);
+
+	ASSERT_NE(setns(self->pidfd, CLONE_VM), 0);
+	EXPECT_EQ(errno, EINVAL);
+
+	ASSERT_NE(setns(self->pidfd, CLONE_NEWUSER | CLONE_VM), 0);
+	EXPECT_EQ(errno, EINVAL);
+}
+
+/* Test that we can't attach to a task that has already exited. */
+TEST_F(current_nsset, pidfd_exited_child)
+{
+	int i;
+	pid_t pid;
+
+	ASSERT_NE(setns(self->child_pidfd_exited, CLONE_NEWUSER | CLONE_NEWNET),
+		  0);
+	EXPECT_EQ(errno, ESRCH);
+
+	pid = getpid();
+	for (i = 0; i < PIDFD_NS_MAX; i++) {
+		const struct ns_info *info = &ns_info[i];
+		/* Verify that we haven't changed any namespaces. */
+		if (self->nsfds[i] >= 0)
+			ASSERT_EQ(in_same_namespace(self->nsfds[i], pid, info->name), 1);
+	}
+}
+
+TEST_F(current_nsset, pidfd_incremental_setns)
+{
+	int i;
+	pid_t pid;
+
+	pid = getpid();
+	for (i = 0; i < PIDFD_NS_MAX; i++) {
+		const struct ns_info *info = &ns_info[i];
+		int nsfd;
+
+		if (self->child_nsfds1[i] < 0)
+			continue;
+
+		if (info->flag) {
+			ASSERT_EQ(setns(self->child_pidfd1, info->flag), 0) {
+				TH_LOG("%m - Failed to setns to %s namespace of %d via pidfd %d",
+				       info->name, self->child_pid1,
+				       self->child_pidfd1);
+			}
+		}
+
+		/* Verify that we have changed to the correct namespaces. */
+		if (info->flag == CLONE_NEWPID)
+			nsfd = self->nsfds[i];
+		else
+			nsfd = self->child_nsfds1[i];
+		ASSERT_EQ(in_same_namespace(nsfd, pid, info->name), 1) {
+			TH_LOG("setns failed to place us correctly into %s namespace of %d via pidfd %d",
+			       info->name, self->child_pid1,
+			       self->child_pidfd1);
+		}
+		TH_LOG("Managed to correctly setns to %s namespace of %d via pidfd %d",
+		       info->name, self->child_pid1, self->child_pidfd1);
+	}
+}
+
+TEST_F(current_nsset, nsfd_incremental_setns)
+{
+	int i;
+	pid_t pid;
+
+	pid = getpid();
+	for (i = 0; i < PIDFD_NS_MAX; i++) {
+		const struct ns_info *info = &ns_info[i];
+		int nsfd;
+
+		if (self->child_nsfds1[i] < 0)
+			continue;
+
+		if (info->flag) {
+			ASSERT_EQ(setns(self->child_nsfds1[i], info->flag), 0) {
+				TH_LOG("%m - Failed to setns to %s namespace of %d via nsfd %d",
+				       info->name, self->child_pid1,
+				       self->child_nsfds1[i]);
+			}
+		}
+
+		/* Verify that we have changed to the correct namespaces. */
+		if (info->flag == CLONE_NEWPID)
+			nsfd = self->nsfds[i];
+		else
+			nsfd = self->child_nsfds1[i];
+		ASSERT_EQ(in_same_namespace(nsfd, pid, info->name), 1) {
+			TH_LOG("setns failed to place us correctly into %s namespace of %d via nsfd %d",
+			       info->name, self->child_pid1,
+			       self->child_nsfds1[i]);
+		}
+		TH_LOG("Managed to correctly setns to %s namespace of %d via nsfd %d",
+		       info->name, self->child_pid1, self->child_nsfds1[i]);
+	}
+}
+
+TEST_F(current_nsset, pidfd_one_shot_setns)
+{
+	unsigned flags = 0;
+	int i;
+	pid_t pid;
+
+	for (i = 0; i < PIDFD_NS_MAX; i++) {
+		const struct ns_info *info = &ns_info[i];
+
+		if (self->child_nsfds1[i] < 0)
+			continue;
+
+		flags |= info->flag;
+		TH_LOG("Adding %s namespace of %d to list of namespaces to attach to",
+		       info->name, self->child_pid1);
+	}
+
+	ASSERT_EQ(setns(self->child_pidfd1, flags), 0) {
+		TH_LOG("%m - Failed to setns to namespaces of %d",
+		       self->child_pid1);
+	}
+
+	pid = getpid();
+	for (i = 0; i < PIDFD_NS_MAX; i++) {
+		const struct ns_info *info = &ns_info[i];
+		int nsfd;
+
+		if (self->child_nsfds1[i] < 0)
+			continue;
+
+		/* Verify that we have changed to the correct namespaces. */
+		if (info->flag == CLONE_NEWPID)
+			nsfd = self->nsfds[i];
+		else
+			nsfd = self->child_nsfds1[i];
+		ASSERT_EQ(in_same_namespace(nsfd, pid, info->name), 1) {
+			TH_LOG("setns failed to place us correctly into %s namespace of %d",
+			       info->name, self->child_pid1);
+		}
+		TH_LOG("Managed to correctly setns to %s namespace of %d",
+		       info->name, self->child_pid1);
+	}
+}
+
+TEST_F(current_nsset, no_foul_play)
+{
+	unsigned flags = 0;
+	int i;
+
+	for (i = 0; i < PIDFD_NS_MAX; i++) {
+		const struct ns_info *info = &ns_info[i];
+
+		if (self->child_nsfds1[i] < 0)
+			continue;
+
+		flags |= info->flag;
+		if (info->flag) /* No use logging pid_for_children. */
+			TH_LOG("Adding %s namespace of %d to list of namespaces to attach to",
+			       info->name, self->child_pid1);
+	}
+
+	ASSERT_EQ(setns(self->child_pidfd1, flags), 0) {
+		TH_LOG("%m - Failed to setns to namespaces of %d vid pidfd %d",
+		       self->child_pid1, self->child_pidfd1);
+	}
+
+	/*
+	 * Can't setns to a user namespace outside of our hierarchy since we
+	 * don't have caps in there and didn't create it. That means that under
+	 * no circumstances should we be able to setns to any of the other
+	 * ones since they aren't owned by our user namespace.
+	 */
+	for (i = 0; i < PIDFD_NS_MAX; i++) {
+		const struct ns_info *info = &ns_info[i];
+
+		if (self->child_nsfds2[i] < 0 || !info->flag)
+			continue;
+
+		ASSERT_NE(setns(self->child_pidfd2, info->flag), 0) {
+			TH_LOG("Managed to setns to %s namespace of %d via pidfd %d",
+			       info->name, self->child_pid2,
+			       self->child_pidfd2);
+		}
+		TH_LOG("%m - Correctly failed to setns to %s namespace of %d via pidfd %d",
+		       info->name, self->child_pid2,
+		       self->child_pidfd2);
+
+		ASSERT_NE(setns(self->child_nsfds2[i], info->flag), 0) {
+			TH_LOG("Managed to setns to %s namespace of %d via nsfd %d",
+			       info->name, self->child_pid2,
+			       self->child_nsfds2[i]);
+		}
+		TH_LOG("%m - Correctly failed to setns to %s namespace of %d via nsfd %d",
+		       info->name, self->child_pid2,
+		       self->child_nsfds2[i]);
+	}
+}
+
+TEST_HARNESS_MAIN