Test the pidfs inode ownership reporting (via fstat) and the permission model (via user.* xattr operations that trigger pidfs_permission()): Ownership tests: - owner_self: own pidfd reports caller's euid/egid - owner_child: child pidfd reports correct ownership - owner_child_changed_euid: ownership tracks live credential changes - owner_exited_child: ownership persists after exit and reap - owner_exited_child_changed_euid: exit_cred preserves changed credentials Permission tests: - permission_same_user: same-user xattr access succeeds (EOPNOTSUPP) - permission_different_user_denied: cross-user access denied (EPERM) - permission_kthread: kernel thread access always denied (EPERM) The user.* xattr namespace is used to exercise pidfs_permission() from userspace: xattr_permission() calls inode_permission() for user.* on S_IFREG inodes, so fgetxattr() returns EOPNOTSUPP when permission is granted (no handler) and EPERM when denied. Tests requiring root skip gracefully via SKIP(). Signed-off-by: Christian Brauner --- tools/testing/selftests/pidfd/.gitignore | 1 + tools/testing/selftests/pidfd/Makefile | 2 +- .../selftests/pidfd/pidfd_inode_owner_test.c | 289 +++++++++++++++++++++ 3 files changed, 291 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/pidfd/.gitignore b/tools/testing/selftests/pidfd/.gitignore index 144e7ff65d6a..1981d39fe3dc 100644 --- a/tools/testing/selftests/pidfd/.gitignore +++ b/tools/testing/selftests/pidfd/.gitignore @@ -12,3 +12,4 @@ pidfd_info_test pidfd_exec_helper pidfd_xattr_test pidfd_setattr_test +pidfd_inode_owner_test diff --git a/tools/testing/selftests/pidfd/Makefile b/tools/testing/selftests/pidfd/Makefile index 764a8f9ecefa..904c9fd595c1 100644 --- a/tools/testing/selftests/pidfd/Makefile +++ b/tools/testing/selftests/pidfd/Makefile @@ -4,7 +4,7 @@ CFLAGS += -g $(KHDR_INCLUDES) $(TOOLS_INCLUDES) -pthread -Wall TEST_GEN_PROGS := pidfd_test pidfd_fdinfo_test pidfd_open_test \ pidfd_poll_test pidfd_wait pidfd_getfd_test pidfd_setns_test \ pidfd_file_handle_test pidfd_bind_mount pidfd_info_test \ - pidfd_xattr_test pidfd_setattr_test + pidfd_xattr_test pidfd_setattr_test pidfd_inode_owner_test TEST_GEN_PROGS_EXTENDED := pidfd_exec_helper diff --git a/tools/testing/selftests/pidfd/pidfd_inode_owner_test.c b/tools/testing/selftests/pidfd/pidfd_inode_owner_test.c new file mode 100644 index 000000000000..58666b87638b --- /dev/null +++ b/tools/testing/selftests/pidfd/pidfd_inode_owner_test.c @@ -0,0 +1,289 @@ +// SPDX-License-Identifier: GPL-2.0 + +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "pidfd.h" +#include "kselftest_harness.h" + +FIXTURE(pidfs_inode_owner) +{ + pid_t child_pid; + int child_pidfd; +}; + +FIXTURE_SETUP(pidfs_inode_owner) +{ + int pipe_fds[2]; + char buf; + + self->child_pid = -1; + self->child_pidfd = -1; + + ASSERT_EQ(pipe(pipe_fds), 0); + + self->child_pid = create_child(&self->child_pidfd, 0); + ASSERT_GE(self->child_pid, 0); + + if (self->child_pid == 0) { + close(pipe_fds[0]); + write_nointr(pipe_fds[1], "c", 1); + close(pipe_fds[1]); + pause(); + _exit(EXIT_SUCCESS); + } + + close(pipe_fds[1]); + ASSERT_EQ(read_nointr(pipe_fds[0], &buf, 1), 1); + close(pipe_fds[0]); +} + +FIXTURE_TEARDOWN(pidfs_inode_owner) +{ + if (self->child_pid > 0) { + kill(self->child_pid, SIGKILL); + sys_waitid(P_PID, self->child_pid, NULL, WEXITED); + } + if (self->child_pidfd >= 0) + close(self->child_pidfd); +} + +/* Own pidfd reports correct ownership. */ +TEST_F(pidfs_inode_owner, owner_self) +{ + int pidfd; + struct stat st; + + pidfd = sys_pidfd_open(getpid(), 0); + ASSERT_GE(pidfd, 0); + + ASSERT_EQ(fstat(pidfd, &st), 0); + EXPECT_EQ(st.st_uid, geteuid()); + EXPECT_EQ(st.st_gid, getegid()); + + close(pidfd); +} + +/* Child pidfd reports correct ownership. */ +TEST_F(pidfs_inode_owner, owner_child) +{ + struct stat st; + + ASSERT_EQ(fstat(self->child_pidfd, &st), 0); + EXPECT_EQ(st.st_uid, geteuid()); + EXPECT_EQ(st.st_gid, getegid()); +} + +/* Ownership tracks credential changes in a live task. */ +TEST_F(pidfs_inode_owner, owner_child_changed_euid) +{ + pid_t pid; + int pidfd, pipe_fds[2]; + struct stat st; + char buf; + + if (getuid() != 0) + SKIP(return, "Test requires root"); + + ASSERT_EQ(pipe(pipe_fds), 0); + + pid = create_child(&pidfd, 0); + ASSERT_GE(pid, 0); + + if (pid == 0) { + close(pipe_fds[0]); + if (setresgid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + if (setresuid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + write_nointr(pipe_fds[1], "c", 1); + close(pipe_fds[1]); + pause(); + _exit(EXIT_SUCCESS); + } + + close(pipe_fds[1]); + ASSERT_EQ(read_nointr(pipe_fds[0], &buf, 1), 1); + close(pipe_fds[0]); + + ASSERT_EQ(fstat(pidfd, &st), 0); + EXPECT_EQ(st.st_uid, (uid_t)65534); + EXPECT_EQ(st.st_gid, (gid_t)65534); + + kill(pid, SIGKILL); + sys_waitid(P_PID, pid, NULL, WEXITED); + close(pidfd); +} + +/* Ownership persists after the child exits and is reaped. */ +TEST_F(pidfs_inode_owner, owner_exited_child) +{ + pid_t pid; + int pidfd; + struct stat st; + + pid = create_child(&pidfd, 0); + ASSERT_GE(pid, 0); + + if (pid == 0) + _exit(EXIT_SUCCESS); + + ASSERT_EQ(sys_waitid(P_PID, pid, NULL, WEXITED), 0); + + ASSERT_EQ(fstat(pidfd, &st), 0); + EXPECT_EQ(st.st_uid, geteuid()); + EXPECT_EQ(st.st_gid, getegid()); + + close(pidfd); +} + +/* Exit credentials preserve changed credentials. */ +TEST_F(pidfs_inode_owner, owner_exited_child_changed_euid) +{ + pid_t pid; + int pidfd; + struct stat st; + + if (getuid() != 0) + SKIP(return, "Test requires root"); + + pid = create_child(&pidfd, 0); + ASSERT_GE(pid, 0); + + if (pid == 0) { + if (setresgid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + if (setresuid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + _exit(EXIT_SUCCESS); + } + + ASSERT_EQ(sys_waitid(P_PID, pid, NULL, WEXITED), 0); + + ASSERT_EQ(fstat(pidfd, &st), 0); + EXPECT_EQ(st.st_uid, (uid_t)65534); + EXPECT_EQ(st.st_gid, (gid_t)65534); + + close(pidfd); +} + +/* Same-user cross-process permission check succeeds. */ +TEST_F(pidfs_inode_owner, permission_same_user) +{ + pid_t pid; + int pidfd; + pid_t parent_pid = getpid(); + + pid = create_child(&pidfd, 0); + ASSERT_GE(pid, 0); + + if (pid == 0) { + int fd; + char buf; + + fd = sys_pidfd_open(parent_pid, 0); + if (fd < 0) + _exit(PIDFD_ERROR); + + /* + * user.* xattr access triggers pidfs_permission(). + * Same user passes may_signal_creds() and + * generic_permission(), so we get EOPNOTSUPP + * (no user.* xattr handler) instead of EPERM. + */ + if (fgetxattr(fd, "user.test", &buf, sizeof(buf)) < 0 && + errno == EOPNOTSUPP) { + close(fd); + _exit(PIDFD_PASS); + } + + close(fd); + _exit(PIDFD_FAIL); + } + + ASSERT_EQ(wait_for_pid(pid), PIDFD_PASS); + close(pidfd); +} + +/* Cross-user access is denied without signal permission. */ +TEST_F(pidfs_inode_owner, permission_different_user_denied) +{ + pid_t pid; + int pidfd; + + if (getuid() != 0) + SKIP(return, "Test requires root"); + + pid = create_child(&pidfd, 0); + ASSERT_GE(pid, 0); + + if (pid == 0) { + int fd; + char buf; + + /* Drop to uid/gid 65534 and lose all capabilities. */ + if (setresgid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + if (setresuid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + + /* Open pidfd for init (uid 0). */ + fd = sys_pidfd_open(1, 0); + if (fd < 0) + _exit(PIDFD_ERROR); + + /* + * uid 65534 cannot signal uid 0 (no CAP_KILL), + * so pidfs_permission() denies access. + */ + if (fgetxattr(fd, "user.test", &buf, sizeof(buf)) < 0 && + errno == EPERM) { + close(fd); + _exit(PIDFD_PASS); + } + + close(fd); + _exit(PIDFD_FAIL); + } + + ASSERT_EQ(wait_for_pid(pid), PIDFD_PASS); + close(pidfd); +} + +/* Kernel thread access is always denied. */ +TEST_F(pidfs_inode_owner, permission_kthread) +{ + int pidfd; + struct stat st; + char buf; + + /* pid 2 is kthreadd. */ + pidfd = sys_pidfd_open(2, 0); + ASSERT_GE(pidfd, 0); + + /* pidfs_permission() returns EPERM for kernel threads. */ + ASSERT_LT(fgetxattr(pidfd, "user.test", &buf, sizeof(buf)), 0); + EXPECT_EQ(errno, EPERM); + + /* fstat bypasses permission and reports root ownership. */ + ASSERT_EQ(fstat(pidfd, &st), 0); + EXPECT_EQ(st.st_uid, (uid_t)0); + EXPECT_EQ(st.st_gid, (gid_t)0); + + close(pidfd); +} + +TEST_HARNESS_MAIN -- 2.47.3