Abhinav Saxena <[email protected]> writes: > TIOCSTI is a TTY ioctl command that allows inserting characters into > the terminal input queue, making it appear as if the user typed those > characters. This functionality has behavior that varies based on system > configuration and process credentials. > > The dev.tty.legacy_tiocsti sysctl introduced in commit 83efeeeb3d04 > (“tty: Allow TIOCSTI to be disabled”) controls TIOCSTI usage. When > disabled, TIOCSTI requires CAP_SYS_ADMIN capability. > > The current implementation checks the current process’s credentials via > capable(CAP_SYS_ADMIN), but does not validate against the file opener’s > credentials stored in file->f_cred. This creates different behavior when > file descriptors are passed between processes via SCM_RIGHTS. > > Add a test suite with 16 test variants using fixture variants to verify > TIOCSTI behavior when dev.tty.legacy_tiocsti is enabled/disabled: > > - Basic TIOCSTI tests (8 variants): Direct testing with different > capability and controlling terminal combinations > - FD passing tests (8 variants): Test behavior when file descriptors > are passed between processes with different capabilities > > The FD passing tests document this behavior - some tests show different > results than expected based on file opener credentials, demonstrating > that TIOCSTI uses current process credentials rather than file opener > credentials. > > The tests validate proper enforcement of the legacy_tiocsti sysctl. Test > implementation uses openpty(3) with TIOCSCTTY for isolated PTY > environments. See tty_ioctl(4) for details on TIOCSTI behavior and > security requirements. > > Signed-off-by: Abhinav Saxena <[email protected]> > — > RESEND: add TTY/serial maintainers and linux-serial CCs. No code changes. > - Link to orignal v4: > <https://lore.kernel.org/r/[email protected]> > > Changes in v4: > - Moved skip conditions and sysctl setup from TEST_F to FIXTURE_SETUP (Kees > Cook) > - Fixed fclose() error handling in set_legacy_tiocsti_setting (Kees Cook) > - Extracted run_basic_tiocsti_test() and run_fdpass_tiocsti_test functions > (Kees Cook) > - Removed redundant sysctl restore logic from TEST_F (Kees Cook) > - Simplified FIXTURE_TEARDOWN (Kees Cook) > - Replace drop_to_nobody() to drop_all_privs() which should be more portable > (Justin Stitt) > - Link to v3: > <https://lore.kernel.org/r/[email protected]> > > Add selftests for TIOCSTI ioctl > > To run all tests: > $ sudo ./tools/testing/selftests/tty/tty_tiocsti_test > > Test Results: > - PASSED: 13/16 tests > - Different behavior: 3/16 tests (documenting credential checking behavior) > > All tests validated using: > - scripts/checkpatch.pl –strict (clean output) > - Functional testing on kernel v6.16-rc2 > > Changes in v3: > - Replaced all printf() calls with TH_LOG() for proper test logging (Kees > Cook) > - Added struct __test_metadata parameter to helper functions > - Moved common legacy_tiocsti availability check to FIXTURE_SETUP() > - Implemented sysctl modification/restoration in FIXTURE_SETUP/TEARDOWN > - Used openpty() with TIOCSCTTY for reliable PTY testing environment > - Fixed child/parent synchronization in FD passing tests > - Replaced manual _exit(1) handling with proper ASSERT statements > - Switched // comments to /* */ format throughout > - Expanded to 16 test variants using fixture variants > - Enhanced error handling and test reliability > - Link to v2: > <https://lore.kernel.org/r/[email protected]> > - Link to v1: > <https://lore.kernel.org/r/[email protected]> > > References: > - tty_ioctl(4) - documents TIOCSTI ioctl and capability requirements > - openpty(3) - pseudo-terminal creation and management > - commit 83efeeeb3d04 (“tty: Allow TIOCSTI to be disabled”) > - Documentation/security/credentials.rst > - <https://github.com/KSPP/linux/issues/156> > - <https://lore.kernel.org/linux-hardening/Y0m9l52AKmw6Yxi1@hostpad/> > - drivers/tty/Kconfig > - Documentation/driver-api/tty/ > — > tools/testing/selftests/tty/Makefile | 6 +- > tools/testing/selftests/tty/config | 1 + > tools/testing/selftests/tty/tty_tiocsti_test.c | 650 > +++++++++++++++++++++++++ > 3 files changed, 656 insertions(+), 1 deletion(-) > > diff –git a/tools/testing/selftests/tty/Makefile > b/tools/testing/selftests/tty/Makefile > index > 50d7027b2ae3fb495dd1c0684363fa8f426be42c..7f6fbe5a0cd5663310e334d9d068b21dab9136ec > 100644 > — a/tools/testing/selftests/tty/Makefile > +++ b/tools/testing/selftests/tty/Makefile > @@ -1,5 +1,9 @@ > # SPDX-License-Identifier: GPL-2.0 > CFLAGS = -O2 -Wall > -TEST_GEN_PROGS := tty_tstamp_update > +TEST_GEN_PROGS := tty_tstamp_update tty_tiocsti_test > +LDLIBS += -lcap > > include ../lib.mk > + > +# Add libcap for TIOCSTI test > +$(OUTPUT)/tty_tiocsti_test: LDLIBS += -lcap > diff –git a/tools/testing/selftests/tty/config > b/tools/testing/selftests/tty/config > new file mode 100644 > index > 0000000000000000000000000000000000000000..c6373aba66366c82435bb26c019eb360eb6310eb > — /dev/null > +++ b/tools/testing/selftests/tty/config > @@ -0,0 +1 @@ > +CONFIG_LEGACY_TIOCSTI=y > diff –git a/tools/testing/selftests/tty/tty_tiocsti_test.c > b/tools/testing/selftests/tty/tty_tiocsti_test.c > new file mode 100644 > index > 0000000000000000000000000000000000000000..5e767e6cb3ef8f05c5430eb0fcc792064c446c03 > — /dev/null > +++ b/tools/testing/selftests/tty/tty_tiocsti_test.c > @@ -0,0 +1,650 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * TTY Tests - TIOCSTI > + * > + * Copyright © 2025 Abhinav Saxena <[email protected]> > + */ > + > +#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 > > — > base-commit: e6b9dce0aeeb91dfc0974ab87f02454e24566182 > change-id: 20250618-toicsti-bug-7822b8e94a32 > > Best regards,
Hi TTY Maintainers, I had submitted this patch series a couple of weeks ago and wanted to gently ping to see if you’ve had a chance to review it. Also, if you have any other concerns or questions, I would be happy to address them. Best, Abhinav
