// SPDX-License-Identifier: GPL-2.0
/*
 * TTY Tests - TIOCSTI
 *
 * Copyright © 2025 Abhinav Saxena <xandfury@gmail.com>
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <errno.h>
#include <stdbool.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <pwd.h>
#include <termios.h>
#include <grp.h>
#include <sys/capability.h>
#include <sys/prctl.h>
#include <pty.h>
#include <utmp.h>

#include "../kselftest_harness.h"

enum test_type {
        TEST_PTY_TIOCSTI_BASIC,
        TEST_PTY_TIOCSTI_FD_PASSING,
        /* other tests cases such as serial may be added. */
};

/*
 * Test Strategy:
 * - Basic tests: Use PTY with/without TIOCSCTTY (controlling terminal for
 *   current process)
 * - FD passing tests: Child creates PTY, parent receives FD (demonstrates
 *   security issue)
 *
 * SECURITY VULNERABILITY DEMONSTRATION:
 * FD passing tests show that TIOCSTI uses CURRENT process credentials, not
 * opener credentials. This means privileged processes can be given FDs from
 * unprivileged processes and successfully perform TIOCSTI operations that the
 * unprivileged process couldn't do directly.
 *
 * Attack scenario:
 * 1. Unprivileged process opens TTY (direct TIOCSTI fails due to lack of
 *    privileges)
 * 2. Unprivileged process passes FD to privileged process via SCM_RIGHTS
 * 3. Privileged process can use TIOCSTI on the FD (succeeds due to its
 *    privileges)
 * 4. Result: Effective privilege escalation via file descriptor passing
 *
 * This matches the kernel logic in tiocsti():
 * 1. if (!tty_legacy_tiocsti && !capable(CAP_SYS_ADMIN)) return -EIO;
 * 2. if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN))
 *        return -EPERM;
 * Note: Both checks use capable() on CURRENT process, not FD opener!
 *
 * If the file credentials were also checked along with the capable() checks
 * then the results for FD pass tests would be consistent with the basic tests.
 */

FIXTURE(tiocsti)
{
        int pty_master_fd; /* PTY - for basic tests */
        int pty_slave_fd;
        bool has_pty;
        bool initial_cap_sys_admin;
        int original_legacy_tiocsti_setting;
        bool can_modify_sysctl;
};

FIXTURE_VARIANT(tiocsti)
{
        const enum test_type test_type;
        const bool controlling_tty; /* true=current->signal->tty == tty */
        const int legacy_tiocsti; /* 0=restricted, 1=permissive */
        const bool requires_cap; /* true=with CAP_SYS_ADMIN, false=without */
        const int expected_success; /* 0=success, -EIO/-EPERM=specific error */
};

/*
 * Tests Controlling Terminal Variants (current->signal->tty == tty)
 *
 * TIOCSTI Test Matrix:
 *
 * | legacy_tiocsti | CAP_SYS_ADMIN | Expected Result | Error |
 * |----------------|---------------|-----------------|-------|
 * | 1 (permissive) | true          | SUCCESS         | -     |
 * | 1 (permissive) | false         | SUCCESS         | -     |
 * | 0 (restricted) | true          | SUCCESS         | -     |
 * | 0 (restricted) | false         | FAILURE         | -EIO  |
 */

/* clang-format off */
FIXTURE_VARIANT_ADD(tiocsti, basic_pty_permissive_withcap) {
        .test_type = TEST_PTY_TIOCSTI_BASIC,
        .controlling_tty = true,
        .legacy_tiocsti = 1,
        .requires_cap = true,
        .expected_success = 0,
};

FIXTURE_VARIANT_ADD(tiocsti, basic_pty_permissive_nocap) {
        .test_type = TEST_PTY_TIOCSTI_BASIC,
        .controlling_tty = true,
        .legacy_tiocsti = 1,
        .requires_cap = false,
        .expected_success = 0,
};

FIXTURE_VARIANT_ADD(tiocsti, basic_pty_restricted_withcap) {
        .test_type = TEST_PTY_TIOCSTI_BASIC,
        .controlling_tty = true,
        .legacy_tiocsti = 0,
        .requires_cap = true,
        .expected_success = 0,
};

FIXTURE_VARIANT_ADD(tiocsti, basic_pty_restricted_nocap) {
        .test_type = TEST_PTY_TIOCSTI_BASIC,
        .controlling_tty = true,
        .legacy_tiocsti = 0,
        .requires_cap = false,
        .expected_success = -EIO, /* FAILURE: legacy restriction */
}; /* clang-format on */

/*
 * Note for FD Passing Test Variants
 * Since we're testing the scenario where an unprivileged process pass an FD
 * to a privileged one, .requires_cap here means the caps of the child process.
 * Not the parent; parent would always be privileged.
 */

/* clang-format off */
FIXTURE_VARIANT_ADD(tiocsti, fdpass_pty_permissive_withcap) {
        .test_type = TEST_PTY_TIOCSTI_FD_PASSING,
        .controlling_tty = true,
        .legacy_tiocsti = 1,
        .requires_cap = true,
        .expected_success = 0,
};

FIXTURE_VARIANT_ADD(tiocsti, fdpass_pty_permissive_nocap) {
        .test_type = TEST_PTY_TIOCSTI_FD_PASSING,
        .controlling_tty = true,
        .legacy_tiocsti = 1,
        .requires_cap = false,
        .expected_success = 0,
};

FIXTURE_VARIANT_ADD(tiocsti, fdpass_pty_restricted_withcap) {
        .test_type = TEST_PTY_TIOCSTI_FD_PASSING,
        .controlling_tty = true,
        .legacy_tiocsti = 0,
        .requires_cap = true,
        .expected_success = 0,
};

FIXTURE_VARIANT_ADD(tiocsti, fdpass_pty_restricted_nocap) {
        .test_type = TEST_PTY_TIOCSTI_FD_PASSING,
        .controlling_tty = true,
        .legacy_tiocsti = 0,
        .requires_cap = false,
        .expected_success = -EIO,
}; /* clang-format on */

/*
 * Non-Controlling Terminal Variants (current->signal->tty != tty)
 *
 * TIOCSTI Test Matrix:
 *
 * | legacy_tiocsti | CAP_SYS_ADMIN | Expected Result | Error |
 * |----------------|---------------|-----------------|-------|
 * | 1 (permissive) | true          | SUCCESS         | -     |
 * | 1 (permissive) | false         | FAILURE         | -EPERM|
 * | 0 (restricted) | true          | SUCCESS         | -     |
 * | 0 (restricted) | false         | FAILURE         | -EIO  |
 */

/* clang-format off */
FIXTURE_VARIANT_ADD(tiocsti, basic_nopty_permissive_withcap) {
        .test_type = TEST_PTY_TIOCSTI_BASIC,
        .controlling_tty = false,
        .legacy_tiocsti = 1,
        .requires_cap = true,
        .expected_success = 0,
};

FIXTURE_VARIANT_ADD(tiocsti, basic_nopty_permissive_nocap) {
        .test_type = TEST_PTY_TIOCSTI_BASIC,
        .controlling_tty = false,
        .legacy_tiocsti = 1,
        .requires_cap = false,
        .expected_success = -EPERM,
};

FIXTURE_VARIANT_ADD(tiocsti, basic_nopty_restricted_withcap) {
        .test_type = TEST_PTY_TIOCSTI_BASIC,
        .controlling_tty = false,
        .legacy_tiocsti = 0,
        .requires_cap = true,
        .expected_success = 0,
};

FIXTURE_VARIANT_ADD(tiocsti, basic_nopty_restricted_nocap) {
        .test_type = TEST_PTY_TIOCSTI_BASIC,
        .controlling_tty = false,
        .legacy_tiocsti = 0,
        .requires_cap = false,
        .expected_success = -EIO,
};

FIXTURE_VARIANT_ADD(tiocsti, fdpass_nopty_permissive_withcap) {
        .test_type = TEST_PTY_TIOCSTI_FD_PASSING,
        .controlling_tty = false,
        .legacy_tiocsti = 1,
        .requires_cap = true,
        .expected_success = 0,
};

FIXTURE_VARIANT_ADD(tiocsti, fdpass_nopty_permissive_nocap) {
        .test_type = TEST_PTY_TIOCSTI_FD_PASSING,
        .controlling_tty = false,
        .legacy_tiocsti = 1,
        .requires_cap = false,
        .expected_success = -EPERM,
};

FIXTURE_VARIANT_ADD(tiocsti, fdpass_nopty_restricted_withcap) {
        .test_type = TEST_PTY_TIOCSTI_FD_PASSING,
        .controlling_tty = false,
        .legacy_tiocsti = 0,
        .requires_cap = true,
        .expected_success = 0,
};

FIXTURE_VARIANT_ADD(tiocsti, fdpass_nopty_restricted_nocap) {
        .test_type = TEST_PTY_TIOCSTI_FD_PASSING,
        .controlling_tty = false,
        .legacy_tiocsti = 0,
        .requires_cap = false,
        .expected_success = -EIO,
}; /* clang-format on */

/* Helper function to send FD via SCM_RIGHTS */
static int send_fd_via_socket(int socket_fd, int fd_to_send)
{
        struct msghdr msg = { 0 };
        struct cmsghdr *cmsg;
        char cmsg_buf[CMSG_SPACE(sizeof(int))];
        char dummy_data = 'F';
        struct iovec iov = { .iov_base = &dummy_data, .iov_len = 1 };

        msg.msg_iov = &iov;
        msg.msg_iovlen = 1;
        msg.msg_control = cmsg_buf;
        msg.msg_controllen = sizeof(cmsg_buf);

        cmsg = CMSG_FIRSTHDR(&msg);
        cmsg->cmsg_level = SOL_SOCKET;
        cmsg->cmsg_type = SCM_RIGHTS;
        cmsg->cmsg_len = CMSG_LEN(sizeof(int));

        memcpy(CMSG_DATA(cmsg), &fd_to_send, sizeof(int));

        return sendmsg(socket_fd, &msg, 0) < 0 ? -1 : 0;
}

/* Helper function to receive FD via SCM_RIGHTS */
static int recv_fd_via_socket(int socket_fd)
{
        struct msghdr msg = { 0 };
        struct cmsghdr *cmsg;
        char cmsg_buf[CMSG_SPACE(sizeof(int))];
        char dummy_data;
        struct iovec iov = { .iov_base = &dummy_data, .iov_len = 1 };
        int received_fd = -1;

        msg.msg_iov = &iov;
        msg.msg_iovlen = 1;
        msg.msg_control = cmsg_buf;
        msg.msg_controllen = sizeof(cmsg_buf);

        if (recvmsg(socket_fd, &msg, 0) < 0)
                return -1;

        for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
                if (cmsg->cmsg_level == SOL_SOCKET &&
                    cmsg->cmsg_type == SCM_RIGHTS) {
                        memcpy(&received_fd, CMSG_DATA(cmsg), sizeof(int));
                        break;
                }
        }

        return received_fd;
}

static inline bool has_cap_sys_admin(void)
{
        cap_t caps = cap_get_proc();

        if (!caps)
                return false;

        cap_flag_value_t cap_val;
        bool has_cap = (cap_get_flag(caps, CAP_SYS_ADMIN, CAP_EFFECTIVE,
                                     &cap_val) == 0) &&
                       (cap_val == CAP_SET);

        cap_free(caps);
        return has_cap;
}

/*
 * Switch to non-root user and clear all capabilities
 */
static inline bool drop_all_privs(struct __test_metadata *_metadata)
{
        /* Drop supplementary groups */
        ASSERT_EQ(setgroups(0, NULL), 0);

        /* Switch to non-root user */
        ASSERT_EQ(setgid(1000), 0);
        ASSERT_EQ(setuid(1000), 0);

        /* Clear all capabilities */
        cap_t empty = cap_init();

        ASSERT_NE(empty, NULL);
        ASSERT_EQ(cap_set_proc(empty), 0);
        cap_free(empty);

        /* Prevent privilege regain */
        ASSERT_EQ(prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0), 0);

        /* Verify privilege drop */
        ASSERT_FALSE(has_cap_sys_admin());
        return true;
}

static inline int get_legacy_tiocsti_setting(struct __test_metadata *_metadata)
{
        FILE *fp;
        int value = -1;

        fp = fopen("/proc/sys/dev/tty/legacy_tiocsti", "r");
        if (!fp) {
                /* legacy_tiocsti sysctl not available (kernel < 6.2) */
                return -1;
        }

        if (fscanf(fp, "%d", &value) == 1 && fclose(fp) == 0) {
                if (value < 0 || value > 1)
                        value = -1; /* Invalid value */
        } else {
                value = -1; /* Failed to parse */
        }

        return value;
}

static inline bool set_legacy_tiocsti_setting(struct __test_metadata *_metadata,
                                              int value)
{
        FILE *fp;
        bool success = false;

        /* Sanity-check the value */
        ASSERT_GE(value, 0);
        ASSERT_LE(value, 1);

        /*
         * Try to open for writing; if we lack permission, return false so
         * the test harness will skip variants that need to change it
         */
        fp = fopen("/proc/sys/dev/tty/legacy_tiocsti", "w");
        if (!fp)
                return false;

        /* Write the new setting */
        if (fprintf(fp, "%d\n", value) > 0 && fclose(fp) == 0)
                success = true;
        else
                TH_LOG("Failed to write legacy_tiocsti: %s", strerror(errno));

        return success;
}

/*
 * TIOCSTI injection test function
 * @tty_fd: TTY slave file descriptor to test TIOCSTI on
 * Returns: 0 on success, -errno on failure
 */
static inline int test_tiocsti_injection(struct __test_metadata *_metadata,
                                         int tty_fd)
{
        int ret;
        char inject_char = 'V';

        errno = 0;
        ret = ioctl(tty_fd, TIOCSTI, &inject_char);
        return ret == 0 ? 0 : -errno;
}

/*
 * Child process: test TIOCSTI directly with capability/controlling
 * terminal setup
 */
static void run_basic_tiocsti_test(struct __test_metadata *_metadata,
                                   FIXTURE_DATA(tiocsti) * self,
                                   const FIXTURE_VARIANT(tiocsti) * variant)
{
        /* Handle capability requirements */
        if (self->initial_cap_sys_admin && !variant->requires_cap)
                ASSERT_TRUE(drop_all_privs(_metadata));

        if (variant->controlling_tty) {
                /*
                 * Create new session and set PTY as
                 * controlling terminal
                 */
                pid_t sid = setsid();

                ASSERT_GE(sid, 0);
                ASSERT_EQ(ioctl(self->pty_slave_fd, TIOCSCTTY, 0), 0);
        }

        /*
         * Validate test environment setup and verify final
         * capability state matches expectation
         * after potential drop.
         */
        ASSERT_TRUE(self->has_pty);
        ASSERT_EQ(has_cap_sys_admin(), variant->requires_cap);

        /* Test TIOCSTI and validate result */
        int result = test_tiocsti_injection(_metadata, self->pty_slave_fd);

        /* Check against expected result from variant */
        EXPECT_EQ(result, variant->expected_success);
        _exit(0);
}

/*
 * Child process: create PTY and then pass FD to parent via SCM_RIGHTS
 */
static void run_fdpass_tiocsti_test(struct __test_metadata *_metadata,
                                    const FIXTURE_VARIANT(tiocsti) * variant,
                                    int sockfd)
{
        signal(SIGHUP, SIG_IGN);

        /* Handle privilege dropping */
        if (!variant->requires_cap && has_cap_sys_admin())
                ASSERT_TRUE(drop_all_privs(_metadata));

        /* Create child's PTY */
        int child_master_fd, child_slave_fd;

        ASSERT_EQ(openpty(&child_master_fd, &child_slave_fd, NULL, NULL, NULL),
                  0);

        if (variant->controlling_tty) {
                pid_t sid = setsid();

                ASSERT_GE(sid, 0);
                ASSERT_EQ(ioctl(child_slave_fd, TIOCSCTTY, 0), 0);
        }

        /* Test child's direct TIOCSTI for reference */
        int direct_result = test_tiocsti_injection(_metadata, child_slave_fd);

        EXPECT_EQ(direct_result, variant->expected_success);

        /* Send FD to parent */
        ASSERT_EQ(send_fd_via_socket(sockfd, child_slave_fd), 0);

        /* Wait for parent completion signal */
        char sync_byte;
        ssize_t bytes_read = read(sockfd, &sync_byte, 1);

        ASSERT_EQ(bytes_read, 1);

        close(child_master_fd);
        close(child_slave_fd);
        close(sockfd);
        _exit(0);
}

FIXTURE_SETUP(tiocsti)
{
        /* Create PTY pair for basic tests */
        self->has_pty = (openpty(&self->pty_master_fd, &self->pty_slave_fd,
                                 NULL, NULL, NULL) == 0);
        if (!self->has_pty) {
                self->pty_master_fd = -1;
                self->pty_slave_fd = -1;
        }

        self->initial_cap_sys_admin = has_cap_sys_admin();
        self->original_legacy_tiocsti_setting =
                get_legacy_tiocsti_setting(_metadata);

        if (self->original_legacy_tiocsti_setting < 0)
                SKIP(return,
                           "legacy_tiocsti sysctl not available (kernel < 6.2)");

        /* Common skip conditions */
        if (variant->test_type == TEST_PTY_TIOCSTI_BASIC && !self->has_pty)
                SKIP(return, "PTY not available for controlling terminal test");

        if (variant->test_type == TEST_PTY_TIOCSTI_FD_PASSING &&
            !self->initial_cap_sys_admin)
                SKIP(return, "FD Pass tests require CAP_SYS_ADMIN");

        if (variant->requires_cap && !self->initial_cap_sys_admin)
                SKIP(return, "Test requires initial CAP_SYS_ADMIN");

        /* Test if we can modify the sysctl (requires appropriate privileges) */
        self->can_modify_sysctl = set_legacy_tiocsti_setting(
                _metadata, self->original_legacy_tiocsti_setting);

        /* Sysctl setup based on variant */
        if (self->can_modify_sysctl &&
            self->original_legacy_tiocsti_setting != variant->legacy_tiocsti) {
                if (!set_legacy_tiocsti_setting(_metadata,
                                                variant->legacy_tiocsti))
                        SKIP(return, "Failed to set legacy_tiocsti sysctl");

        } else if (!self->can_modify_sysctl &&
                   self->original_legacy_tiocsti_setting !=
                           variant->legacy_tiocsti)
                SKIP(return, "legacy_tiocsti setting mismatch");
}

FIXTURE_TEARDOWN(tiocsti)
{
        /*
         * Backup restoration -
         * each test should restore its own sysctl changes
         */
        if (self->can_modify_sysctl) {
                int current_value = get_legacy_tiocsti_setting(_metadata);

                if (current_value != self->original_legacy_tiocsti_setting) {
                        TH_LOG("Backup: Restoring legacy_tiocsti from %d to %d",
                               current_value,
                               self->original_legacy_tiocsti_setting);
                        set_legacy_tiocsti_setting(
                                _metadata,
                                self->original_legacy_tiocsti_setting);
                }
        }

        if (self->has_pty) {
                if (self->pty_master_fd >= 0)
                        close(self->pty_master_fd);
                if (self->pty_slave_fd >= 0)
                        close(self->pty_slave_fd);
        }
}

TEST_F(tiocsti, test)
{
        int status;
        pid_t child_pid;

        if (variant->test_type == TEST_PTY_TIOCSTI_BASIC) {
                /* ===== BASIC TIOCSTI TEST ===== */
                child_pid = fork();
                ASSERT_GE(child_pid, 0);

                /* Perform the actual test in the child process */
                if (child_pid == 0)
                        run_basic_tiocsti_test(_metadata, self, variant);

        } else {
                /* ===== FD PASSING SECURITY TEST ===== */
                int sockpair[2];

                ASSERT_EQ(socketpair(AF_UNIX, SOCK_STREAM, 0, sockpair), 0);

                child_pid = fork();
                ASSERT_GE(child_pid, 0);

                if (child_pid == 0) {
                        /* Child process - create PTY and send FD */
                        close(sockpair[0]);
                        run_fdpass_tiocsti_test(_metadata, variant,
                                                sockpair[1]);
                }

                /* Parent process - receive FD and test TIOCSTI */
                close(sockpair[1]);

                int received_fd = recv_fd_via_socket(sockpair[0]);

                ASSERT_GE(received_fd, 0);

                bool parent_has_cap = self->initial_cap_sys_admin;

                TH_LOG("=== TIOCSTI FD Passing Test Context ===");
                TH_LOG("legacy_tiocsti: %d, Parent CAP_SYS_ADMIN: %s, Child: %s",
                       variant->legacy_tiocsti, parent_has_cap ? "yes" : "no",
                       variant->requires_cap ? "kept" : "dropped");

                /* SECURITY TEST: Try TIOCSTI with FD opened by child */
                int result = test_tiocsti_injection(_metadata, received_fd);

                /* Log security concern if demonstrated */
                if (result == 0 && !variant->requires_cap) {
                        TH_LOG("*** SECURITY CONCERN DEMONSTRATED ***");
                        TH_LOG("Privileged parent can use TIOCSTI on FD from unprivileged child");
                        TH_LOG("This shows current process credentials are used, not opener credentials");
                }

                EXPECT_EQ(result, variant->expected_success)
                {
                        TH_LOG("FD passing: expected error %d, got %d",
                               variant->expected_success, result);
                }

                /* Signal child completion */
                char sync_byte = 'D';
                ssize_t bytes_written = write(sockpair[0], &sync_byte, 1);

                ASSERT_EQ(bytes_written, 1);

                close(received_fd);
                close(sockpair[0]);
        }

        /* Common child process cleanup for both test types */
        ASSERT_EQ(waitpid(child_pid, &status, 0), child_pid);

        if (WIFSIGNALED(status)) {
                TH_LOG("Child terminated by signal %d", WTERMSIG(status));
                ASSERT_FALSE(WIFSIGNALED(status))
                {
                        TH_LOG("Child process failed assertion");
                }
        } else {
                EXPECT_EQ(WEXITSTATUS(status), 0);
        }
}

TEST_HARNESS_MAIN