sandlock_core/

context.rs

// Fork + confinement sequence: child-side Landlock + seccomp application
// and parent-child pipe synchronization.

use std::ffi::CString;
use std::io;
use std::os::fd::{AsRawFd, FromRawFd, OwnedFd, RawFd};
use std::path::PathBuf;

use crate::policy::{FsIsolation, Policy};
use crate::seccomp::bpf::{self, stmt, jump};
use crate::sys::structs::{
    AF_INET, AF_INET6, AF_NETLINK,
    BPF_ABS, BPF_ALU, BPF_AND, BPF_JEQ, BPF_JSET, BPF_JMP, BPF_K, BPF_LD, BPF_RET, BPF_W,
    CLONE_NS_FLAGS, DEFAULT_DENY_SYSCALLS, EPERM, NETLINK_SOCK_DIAG, SECCOMP_RET_ERRNO,
    SOCK_DGRAM, SOCK_RAW, SOCK_TYPE_MASK, TIOCLINUX, TIOCSTI,
    PR_SET_DUMPABLE, PR_SET_SECUREBITS, PR_SET_PTRACER,
    OFFSET_ARGS0_LO, OFFSET_ARGS1_LO, OFFSET_ARGS2_LO, OFFSET_NR,
    SockFilter,
};

// ============================================================
// Pipe pair for parent-child synchronization
// ============================================================

/// Pipes for parent-child communication after fork().
pub struct PipePair {
    /// Parent reads the notif fd number written by the child.
    pub notif_r: OwnedFd,
    /// Child writes the notif fd number to the parent.
    pub notif_w: OwnedFd,
    /// Child reads the "supervisor ready" signal from the parent.
    pub ready_r: OwnedFd,
    /// Parent writes the "supervisor ready" signal to the child.
    pub ready_w: OwnedFd,
}

impl PipePair {
    /// Create two pipe pairs using `pipe2(O_CLOEXEC)`.
    pub fn new() -> io::Result<Self> {
        let mut notif_fds = [0i32; 2];
        let mut ready_fds = [0i32; 2];

        // SAFETY: pipe2 with valid pointers and O_CLOEXEC
        let ret = unsafe { libc::pipe2(notif_fds.as_mut_ptr(), libc::O_CLOEXEC) };
        if ret < 0 {
            return Err(io::Error::last_os_error());
        }

        let ret = unsafe { libc::pipe2(ready_fds.as_mut_ptr(), libc::O_CLOEXEC) };
        if ret < 0 {
            // Close the first pair on failure
            unsafe {
                libc::close(notif_fds[0]);
                libc::close(notif_fds[1]);
            }
            return Err(io::Error::last_os_error());
        }

        // SAFETY: pipe2 returned valid fds
        Ok(PipePair {
            notif_r: unsafe { OwnedFd::from_raw_fd(notif_fds[0]) },
            notif_w: unsafe { OwnedFd::from_raw_fd(notif_fds[1]) },
            ready_r: unsafe { OwnedFd::from_raw_fd(ready_fds[0]) },
            ready_w: unsafe { OwnedFd::from_raw_fd(ready_fds[1]) },
        })
    }
}

// ============================================================
// Pipe I/O helpers
// ============================================================

/// Write a `u32` as 4 little-endian bytes to a raw fd.
pub(crate) fn write_u32_fd(fd: RawFd, val: u32) -> io::Result<()> {
    let buf = val.to_le_bytes();
    let mut written = 0usize;
    while written < 4 {
        let ret = unsafe {
            libc::write(
                fd,
                buf[written..].as_ptr() as *const libc::c_void,
                4 - written,
            )
        };
        if ret < 0 {
            return Err(io::Error::last_os_error());
        }
        written += ret as usize;
    }
    Ok(())
}

/// Read a `u32` (4 little-endian bytes, blocking) from a raw fd.
pub(crate) fn read_u32_fd(fd: RawFd) -> io::Result<u32> {
    let mut buf = [0u8; 4];
    let mut total = 0usize;
    while total < 4 {
        let ret = unsafe {
            libc::read(
                fd,
                buf[total..].as_mut_ptr() as *mut libc::c_void,
                4 - total,
            )
        };
        if ret < 0 {
            return Err(io::Error::last_os_error());
        }
        if ret == 0 {
            return Err(io::Error::new(
                io::ErrorKind::UnexpectedEof,
                "pipe closed before 4 bytes read",
            ));
        }
        total += ret as usize;
    }
    Ok(u32::from_le_bytes(buf))
}

// ============================================================
// Syscall name → number mapping
// ============================================================

/// Map a syscall name to its `libc::SYS_*` number.
///
/// Covers all names in `DEFAULT_DENY_SYSCALLS` plus extras needed for
/// notif and arg-filter lists.
pub fn syscall_name_to_nr(name: &str) -> Option<u32> {
    let nr: i64 = match name {
        "mount" => libc::SYS_mount,
        "umount2" => libc::SYS_umount2,
        "pivot_root" => libc::SYS_pivot_root,
        "swapon" => libc::SYS_swapon,
        "swapoff" => libc::SYS_swapoff,
        "reboot" => libc::SYS_reboot,
        "sethostname" => libc::SYS_sethostname,
        "setdomainname" => libc::SYS_setdomainname,
        "kexec_load" => libc::SYS_kexec_load,
        "init_module" => libc::SYS_init_module,
        "finit_module" => libc::SYS_finit_module,
        "delete_module" => libc::SYS_delete_module,
        "unshare" => libc::SYS_unshare,
        "setns" => libc::SYS_setns,
        "perf_event_open" => libc::SYS_perf_event_open,
        "bpf" => libc::SYS_bpf,
        "userfaultfd" => libc::SYS_userfaultfd,
        "keyctl" => libc::SYS_keyctl,
        "add_key" => libc::SYS_add_key,
        "request_key" => libc::SYS_request_key,
        "ptrace" => libc::SYS_ptrace,
        "process_vm_readv" => libc::SYS_process_vm_readv,
        "process_vm_writev" => libc::SYS_process_vm_writev,
        "open_by_handle_at" => libc::SYS_open_by_handle_at,
        "name_to_handle_at" => libc::SYS_name_to_handle_at,
        "ioperm" => libc::SYS_ioperm,
        "iopl" => libc::SYS_iopl,
        "quotactl" => libc::SYS_quotactl,
        "acct" => libc::SYS_acct,
        "lookup_dcookie" => libc::SYS_lookup_dcookie,
        // nfsservctl was removed in Linux 3.1; no libc constant — skip
        "io_uring_setup" => libc::SYS_io_uring_setup,
        "io_uring_enter" => libc::SYS_io_uring_enter,
        "io_uring_register" => libc::SYS_io_uring_register,
        // Additional syscalls for notif/arg filters
        "clone" => libc::SYS_clone,
        "clone3" => libc::SYS_clone3,
        "vfork" => libc::SYS_vfork,
        "mmap" => libc::SYS_mmap,
        "munmap" => libc::SYS_munmap,
        "brk" => libc::SYS_brk,
        "mremap" => libc::SYS_mremap,
        "connect" => libc::SYS_connect,
        "sendto" => libc::SYS_sendto,
        "sendmsg" => libc::SYS_sendmsg,
        "ioctl" => libc::SYS_ioctl,
        "socket" => libc::SYS_socket,
        "prctl" => libc::SYS_prctl,
        "getrandom" => libc::SYS_getrandom,
        "openat" => libc::SYS_openat,
        "open" => libc::SYS_open,
        "getdents64" => libc::SYS_getdents64,
        "getdents" => libc::SYS_getdents,
        "bind" => libc::SYS_bind,
        "getsockname" => libc::SYS_getsockname,
        "clock_gettime" => libc::SYS_clock_gettime,
        "gettimeofday" => libc::SYS_gettimeofday,
        "time" => libc::SYS_time,
        "clock_nanosleep" => libc::SYS_clock_nanosleep,
        "timerfd_settime" => libc::SYS_timerfd_settime,
        "timer_settime" => libc::SYS_timer_settime,
        "execve" => libc::SYS_execve,
        "execveat" => libc::SYS_execveat,
        // COW filesystem syscalls
        "unlinkat" => libc::SYS_unlinkat,
        "mkdirat" => libc::SYS_mkdirat,
        "renameat2" => libc::SYS_renameat2,
        "newfstatat" => libc::SYS_newfstatat,
        "statx" => libc::SYS_statx,
        "faccessat" => libc::SYS_faccessat,
        "symlinkat" => libc::SYS_symlinkat,
        "linkat" => libc::SYS_linkat,
        "fchmodat" => libc::SYS_fchmodat,
        "fchownat" => libc::SYS_fchownat,
        "readlinkat" => libc::SYS_readlinkat,
        "truncate" => libc::SYS_truncate,
        "utimensat" => libc::SYS_utimensat,
        "unlink" => libc::SYS_unlink,
        "rmdir" => libc::SYS_rmdir,
        "mkdir" => libc::SYS_mkdir,
        "rename" => libc::SYS_rename,
        "stat" => libc::SYS_stat,
        "lstat" => libc::SYS_lstat,
        "access" => libc::SYS_access,
        "symlink" => libc::SYS_symlink,
        "link" => libc::SYS_link,
        "chmod" => libc::SYS_chmod,
        "chown" => libc::SYS_chown,
        "lchown" => libc::SYS_lchown,
        "readlink" => libc::SYS_readlink,
        "futimesat" => libc::SYS_futimesat,
        "fork" => libc::SYS_fork,
        _ => return None,
    };
    Some(nr as u32)
}

// ============================================================
// Policy → syscall lists
// ============================================================

/// Determine which syscalls need `SECCOMP_RET_USER_NOTIF`.
pub fn notif_syscalls(policy: &Policy) -> Vec<u32> {
    let mut nrs = vec![
        libc::SYS_clone as u32,
        libc::SYS_clone3 as u32,
        libc::SYS_vfork as u32,
    ];

    if policy.max_memory.is_some() {
        nrs.push(libc::SYS_mmap as u32);
        nrs.push(libc::SYS_munmap as u32);
        nrs.push(libc::SYS_brk as u32);
        nrs.push(libc::SYS_mremap as u32);
        nrs.push(libc::SYS_shmget as u32);
    }

    if !policy.net_allow_hosts.is_empty() || policy.policy_fn.is_some() {
        nrs.push(libc::SYS_connect as u32);
        nrs.push(libc::SYS_sendto as u32);
        nrs.push(libc::SYS_sendmsg as u32);
        nrs.push(libc::SYS_bind as u32);
    }

    if policy.random_seed.is_some() {
        nrs.push(libc::SYS_getrandom as u32);
        // Also intercept openat so the supervisor can re-patch vDSO after exec.
        nrs.push(libc::SYS_openat as u32);
    }

    if policy.time_start.is_some() {
        nrs.extend_from_slice(&[
            libc::SYS_clock_nanosleep as u32,
            libc::SYS_timerfd_settime as u32,
            libc::SYS_timer_settime as u32,
        ]);
        // Also intercept openat so the supervisor gets a notification after exec
        // and can re-patch the vDSO (exec replaces vDSO with a fresh copy).
        nrs.push(libc::SYS_openat as u32);
    }

    // /proc virtualization needs openat interception
    if policy.num_cpus.is_some() || policy.max_memory.is_some() || policy.isolate_pids || policy.port_remap {
        nrs.push(libc::SYS_openat as u32);
    }
    // Virtualize sched_getaffinity so nproc/sysconf agree with /proc/cpuinfo
    if policy.num_cpus.is_some() {
        nrs.push(libc::SYS_sched_getaffinity as u32);
    }
    if policy.isolate_pids || policy.deterministic_dirs {
        nrs.extend_from_slice(&[
            libc::SYS_getdents64 as u32,
            libc::SYS_getdents as u32,
        ]);
    }
    if policy.hostname.is_some() {
        nrs.push(libc::SYS_uname as u32);
        nrs.push(libc::SYS_openat as u32);
    }

    // COW filesystem interception (seccomp-based, unprivileged)
    if policy.workdir.is_some() && policy.fs_isolation == FsIsolation::None {
        nrs.extend_from_slice(&[
            libc::SYS_openat as u32,
            libc::SYS_unlinkat as u32,
            libc::SYS_mkdirat as u32,
            libc::SYS_renameat2 as u32,
            libc::SYS_symlinkat as u32,
            libc::SYS_linkat as u32,
            libc::SYS_fchmodat as u32,
            libc::SYS_fchownat as u32,
            libc::SYS_truncate as u32,
            libc::SYS_newfstatat as u32,
            libc::SYS_statx as u32,
            libc::SYS_faccessat as u32,
            libc::SYS_readlinkat as u32,
            libc::SYS_getdents64 as u32,
            libc::SYS_getdents as u32,
        ]);
    }

    // Chroot path interception
    if policy.chroot.is_some() {
        nrs.extend_from_slice(&[
            libc::SYS_openat as u32,
            libc::SYS_execve as u32,
            libc::SYS_execveat as u32,
            libc::SYS_unlinkat as u32,
            libc::SYS_mkdirat as u32,
            libc::SYS_renameat2 as u32,
            libc::SYS_symlinkat as u32,
            libc::SYS_linkat as u32,
            libc::SYS_fchmodat as u32,
            libc::SYS_fchownat as u32,
            libc::SYS_truncate as u32,
            libc::SYS_newfstatat as u32,
            libc::SYS_statx as u32,
            libc::SYS_faccessat as u32,
            libc::SYS_readlinkat as u32,
            libc::SYS_getdents64 as u32,
            libc::SYS_getdents as u32,
            libc::SYS_chdir as u32,
            libc::SYS_getcwd as u32,
            libc::SYS_statfs as u32,
            libc::SYS_utimensat as u32,
        ]);
    }

    // Dynamic policy callback — intercept key syscalls for event emission
    if policy.policy_fn.is_some() {
        nrs.extend_from_slice(&[
            libc::SYS_openat as u32,
            libc::SYS_connect as u32,
            libc::SYS_sendto as u32,
            libc::SYS_bind as u32,
            libc::SYS_execve as u32,
            libc::SYS_execveat as u32,
        ]);
    }

    // Port remapping
    if policy.port_remap {
        nrs.extend_from_slice(&[
            libc::SYS_bind as u32,
            libc::SYS_getsockname as u32,
        ]);
    }

    nrs.sort_unstable();
    nrs.dedup();
    nrs
}

/// Resolve `deny_syscalls` names to numbers.
///
/// If both `deny_syscalls` and `allow_syscalls` are `None`, returns the
/// numbers for `DEFAULT_DENY_SYSCALLS`.
pub fn deny_syscall_numbers(policy: &Policy) -> Vec<u32> {
    if let Some(ref names) = policy.deny_syscalls {
        names
            .iter()
            .filter_map(|n| syscall_name_to_nr(n))
            .collect()
    } else if policy.allow_syscalls.is_none() {
        DEFAULT_DENY_SYSCALLS
            .iter()
            .filter_map(|n| syscall_name_to_nr(n))
            .collect()
    } else {
        // allow_syscalls is set — no deny list
        Vec::new()
    }
}

/// Build argument-level seccomp filter instructions matching the Python
/// `_build_arg_filters()` exactly.
///
/// Returns a `Vec<SockFilter>` containing self-contained BPF blocks for:
///   - clone: block namespace creation flags
///   - ioctl: block TIOCSTI, TIOCLINUX
///   - prctl: block PR_SET_DUMPABLE, PR_SET_SECUREBITS, PR_SET_PTRACER
///   - socket: block NETLINK_SOCK_DIAG (with AF_NETLINK domain check)
///   - socket: block SOCK_RAW/SOCK_DGRAM on AF_INET/AF_INET6 (with type mask)
pub fn arg_filters(policy: &Policy) -> Vec<SockFilter> {
    let ret_errno = SECCOMP_RET_ERRNO | EPERM as u32;
    let nr_clone = libc::SYS_clone as u32;
    let nr_ioctl = libc::SYS_ioctl as u32;
    let nr_prctl = libc::SYS_prctl as u32;
    let nr_socket = libc::SYS_socket as u32;

    let mut insns: Vec<SockFilter> = Vec::new();

    // --- clone: block namespace creation flags ---
    // 5 instructions:
    //   LD NR
    //   JEQ clone → +0, skip 3
    //   LD arg0
    //   JSET NS_FLAGS → +0, skip 1
    //   RET ERRNO
    insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_NR));
    insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, nr_clone, 0, 3));
    insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_ARGS0_LO));
    insns.push(jump(BPF_JMP | BPF_JSET | BPF_K, CLONE_NS_FLAGS as u32, 0, 1));
    insns.push(stmt(BPF_RET | BPF_K, ret_errno));

    // --- ioctl: block dangerous commands (TIOCSTI, TIOCLINUX) ---
    // Layout: LD NR, JEQ ioctl (skip 1 + N*2), LD arg1, [JEQ cmd, RET ERRNO] * N
    let dangerous_ioctls: &[u32] = &[TIOCSTI as u32, TIOCLINUX as u32];
    let n_ioctls = dangerous_ioctls.len();
    let skip_count = (1 + n_ioctls * 2) as u8;
    insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_NR));
    insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, nr_ioctl, 0, skip_count));
    insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_ARGS1_LO));
    for &cmd in dangerous_ioctls {
        insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, cmd, 0, 1));
        insns.push(stmt(BPF_RET | BPF_K, ret_errno));
    }

    // --- prctl: block dangerous options ---
    // Layout: LD NR, JEQ prctl (skip 1 + N*2), LD arg0, [JEQ op, RET ERRNO] * N
    let dangerous_prctl_ops: &[u32] = &[PR_SET_DUMPABLE, PR_SET_SECUREBITS, PR_SET_PTRACER];
    let n_ops = dangerous_prctl_ops.len();
    let skip_count = (1 + n_ops * 2) as u8;
    insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_NR));
    insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, nr_prctl, 0, skip_count));
    insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_ARGS0_LO));
    for &op in dangerous_prctl_ops {
        insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, op, 0, 1));
        insns.push(stmt(BPF_RET | BPF_K, ret_errno));
    }

    // --- socket: block NETLINK_SOCK_DIAG (only on AF_NETLINK domain) ---
    // 7 instructions:
    //   LD NR
    //   JEQ socket → +0, skip 5
    //   LD arg0 (domain)
    //   JEQ AF_NETLINK → +0, skip 3
    //   LD arg2 (protocol)
    //   JEQ NETLINK_SOCK_DIAG → +0, skip 1
    //   RET ERRNO
    insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_NR));
    insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, nr_socket, 0, 5));
    insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_ARGS0_LO));
    insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, AF_NETLINK, 0, 3));
    insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_ARGS2_LO));
    insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, NETLINK_SOCK_DIAG, 0, 1));
    insns.push(stmt(BPF_RET | BPF_K, ret_errno));

    // --- socket: block SOCK_RAW and/or SOCK_DGRAM on AF_INET/AF_INET6 ---
    let mut blocked_types: Vec<u32> = Vec::new();
    if policy.no_raw_sockets {
        blocked_types.push(SOCK_RAW);
    }
    if policy.no_udp {
        blocked_types.push(SOCK_DGRAM);
    }

    if !blocked_types.is_empty() {
        let n = blocked_types.len();
        // Instructions after domain checks: 2 (load+AND) + N (JEQs) + 1 (RET)
        let after_domain = 2 + n + 1;
        // Total after NR check: 3 (load domain + 2 JEQs) + after_domain
        let skip_all = (3 + after_domain) as u8;

        insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_NR));
        insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, nr_socket, 0, skip_all));
        // Load domain (arg0)
        insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_ARGS0_LO));
        // AF_INET → skip to type check (jump over AF_INET6 check)
        insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, AF_INET, 1, 0));
        // AF_INET6 → type check; else skip everything remaining
        insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, AF_INET6, 0, after_domain as u8));
        // Load type (arg1) and mask off SOCK_NONBLOCK|SOCK_CLOEXEC
        insns.push(stmt(BPF_LD | BPF_W | BPF_ABS, OFFSET_ARGS1_LO));
        insns.push(stmt(BPF_ALU | BPF_AND | BPF_K, SOCK_TYPE_MASK));
        // Check each blocked type
        for (i, &sock_type) in blocked_types.iter().enumerate() {
            let remaining = n - i - 1;
            // Match → jump to RET ERRNO (skip 'remaining' JEQs ahead)
            // No match on last type → skip past RET ERRNO (jf=1)
            // No match on non-last → check next type (jf=0)
            let jf: u8 = if remaining == 0 { 1 } else { 0 };
            insns.push(jump(BPF_JMP | BPF_JEQ | BPF_K, sock_type, remaining as u8, jf));
        }
        // Deny return (reached by any matching JEQ)
        insns.push(stmt(BPF_RET | BPF_K, ret_errno));
    }

    insns
}

// ============================================================
// Close fds above threshold
// ============================================================

/// Close all file descriptors above `min_fd`, except those in `keep`.
fn close_fds_above(min_fd: RawFd, keep: &[RawFd]) {
    // Read /proc/self/fd to enumerate open fds.
    // Collect all fd numbers first, then close them after dropping the directory
    // iterator. This avoids closing the directory fd during iteration.
    let fds_to_close: Vec<RawFd> = {
        let dir = match std::fs::read_dir("/proc/self/fd") {
            Ok(d) => d,
            Err(_) => return,
        };
        dir.flatten()
            .filter_map(|entry| {
                entry.file_name().into_string().ok()
                    .and_then(|name| name.parse::<RawFd>().ok())
            })
            .filter(|&fd| fd > min_fd && !keep.contains(&fd))
            .collect()
    };
    // The directory is now closed; safe to close the collected fds.
    for fd in fds_to_close {
        unsafe { libc::close(fd) };
    }
}

// ============================================================
// COW filesystem config passed from parent to child
// ============================================================

/// Overlay mount configuration for the child process.
pub(crate) struct CowConfig {
    pub merged: PathBuf,
    pub upper: PathBuf,
    pub work: PathBuf,
    pub lowers: Vec<PathBuf>,
}

/// Write uid/gid maps for an unprivileged user namespace.
/// `real_uid`/`real_gid` must be captured *before* unshare(CLONE_NEWUSER),
/// since getuid()/getgid() return the overflow id (65534) after unshare.
fn write_id_maps(real_uid: u32, real_gid: u32) {
    let _ = std::fs::write("/proc/self/uid_map", format!("0 {} 1\n", real_uid));
    let _ = std::fs::write("/proc/self/setgroups", "deny\n");
    let _ = std::fs::write("/proc/self/gid_map", format!("0 {} 1\n", real_gid));
}

/// Write uid/gid maps using the post-unshare overflow uid (65534).
/// Used by the OverlayFS COW path which relies on this specific mapping.
fn write_id_maps_overflow() {
    let uid = unsafe { libc::getuid() };
    let gid = unsafe { libc::getgid() };
    write_id_maps(uid, gid);
}

// ============================================================
// Child-side confinement (never returns)
// ============================================================

/// Apply irreversible confinement (Landlock + seccomp) then exec the command.
///
/// This function **never returns**: it calls `execvp` on success or
/// `_exit(127)` on any error.
pub(crate) fn confine_child(policy: &Policy, cmd: &[CString], pipes: &PipePair, cow_config: Option<&CowConfig>, nested: bool) -> ! {
    // Helper: abort child on error. Includes the OS error automatically.
    macro_rules! fail {
        ($msg:expr) => {{
            let err = std::io::Error::last_os_error();
            let _ = write!(std::io::stderr(), "sandlock child: {}: {}\n", $msg, err);
            unsafe { libc::_exit(127) };
        }};
    }

    use std::io::Write;

    // 1. New process group
    if unsafe { libc::setpgid(0, 0) } != 0 {
        fail!("setpgid");
    }

    // 1b. If stdin is a terminal, become the foreground process group
    //     so interactive shells can read from the TTY.
    //     Must ignore SIGTTOU first — a background pgrp calling tcsetpgrp
    //     gets stopped by SIGTTOU otherwise.
    if unsafe { libc::isatty(0) } == 1 {
        unsafe {
            libc::signal(libc::SIGTTOU, libc::SIG_IGN);
            libc::tcsetpgrp(0, libc::getpgrp());
            libc::signal(libc::SIGTTOU, libc::SIG_DFL);
        }
    }

    // 2. Die if parent exits
    if unsafe { libc::prctl(libc::PR_SET_PDEATHSIG, libc::SIGKILL) } != 0 {
        fail!("prctl(PR_SET_PDEATHSIG)");
    }

    // 3. Check parent didn't die between fork and prctl
    if unsafe { libc::getppid() } == 1 {
        fail!("parent died before confinement");
    }

    // 4. Optional: disable ASLR
    if policy.no_randomize_memory {
        const ADDR_NO_RANDOMIZE: u64 = 0x0040000;
        if unsafe { libc::personality(ADDR_NO_RANDOMIZE as libc::c_ulong) } == -1 {
            fail!("personality(ADDR_NO_RANDOMIZE)");
        }
    }

    // 4b. Optional: CPU core binding
    if let Some(ref cores) = policy.cpu_cores {
        if !cores.is_empty() {
            let mut set = unsafe { std::mem::zeroed::<libc::cpu_set_t>() };
            unsafe { libc::CPU_ZERO(&mut set) };
            for &core in cores {
                unsafe { libc::CPU_SET(core as usize, &mut set) };
            }
            if unsafe {
                libc::sched_setaffinity(
                    0,
                    std::mem::size_of::<libc::cpu_set_t>(),
                    &set,
                )
            } != 0
            {
                fail!("sched_setaffinity");
            }
        }
    }

    // 5. Optional: disable THP
    if policy.no_huge_pages {
        if unsafe { libc::prctl(libc::PR_SET_THP_DISABLE, 1, 0, 0, 0) } != 0 {
            fail!("prctl(PR_SET_THP_DISABLE)");
        }
    }

    // Capture real uid/gid before any unshare (after unshare they become 65534)
    let real_uid = unsafe { libc::getuid() };
    let real_gid = unsafe { libc::getgid() };

    // 5b. User namespace for privileged mode (fake root) or OverlayFS COW
    if policy.privileged && cow_config.is_none() {
        if unsafe { libc::unshare(libc::CLONE_NEWUSER) } != 0 {
            fail!("unshare(CLONE_NEWUSER)");
        }
        write_id_maps(real_uid, real_gid);
    }

    // 5c. User + mount namespace for OverlayFS COW (includes CLONE_NEWUSER)
    if let Some(ref cow) = cow_config {
        // unshare user + mount namespaces (unprivileged)
        if unsafe { libc::unshare(libc::CLONE_NEWUSER | libc::CLONE_NEWNS) } != 0 {
            fail!("unshare(CLONE_NEWUSER | CLONE_NEWNS)");
        }

        // Write uid/gid maps using overflow uid (preserves existing COW behavior)
        write_id_maps_overflow();

        // Mount the overlay filesystem
        let lowerdir = cow.lowers.iter()
            .map(|p| p.display().to_string())
            .collect::<Vec<_>>()
            .join(":");
        let opts = format!(
            "lowerdir={},upperdir={},workdir={}",
            lowerdir,
            cow.upper.display(),
            cow.work.display(),
        );

        let merged_cstr = match CString::new(cow.merged.to_str().unwrap_or("")) {
            Ok(c) => c,
            Err(_) => fail!("invalid merged path"),
        };
        let overlay_cstr = CString::new("overlay").unwrap();
        let opts_cstr = match CString::new(opts) {
            Ok(c) => c,
            Err(_) => fail!("invalid overlay opts"),
        };

        let ret = unsafe {
            libc::mount(
                overlay_cstr.as_ptr(),
                merged_cstr.as_ptr(),
                overlay_cstr.as_ptr(),
                0,
                opts_cstr.as_ptr() as *const libc::c_void,
            )
        };
        if ret != 0 {
            fail!("mount overlay");
        }
    }

    // 6. Optional: change working directory
    // When chroot is set, default to the chroot root if no workdir specified
    let effective_workdir = if let Some(ref workdir) = policy.workdir {
        if let Some(ref chroot_root) = policy.chroot {
            // Workdir is virtual (child-visible), translate to host path
            Some(chroot_root.join(workdir.strip_prefix("/").unwrap_or(workdir)))
        } else {
            Some(workdir.clone())
        }
    } else if let Some(ref chroot_root) = policy.chroot {
        // Default to chroot root
        Some(chroot_root.clone())
    } else {
        None
    };

    if let Some(ref workdir) = effective_workdir {
        let c_path = match CString::new(workdir.as_os_str().as_encoded_bytes()) {
            Ok(p) => p,
            Err(_) => fail!("invalid workdir path"),
        };
        if unsafe { libc::chdir(c_path.as_ptr()) } != 0 {
            fail!("chdir");
        }
    }

    // 7. Set NO_NEW_PRIVS (required for both Landlock and seccomp without CAP_SYS_ADMIN)
    if unsafe { libc::prctl(libc::PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) } != 0 {
        fail!("prctl(PR_SET_NO_NEW_PRIVS)");
    }

    // 8. Apply Landlock confinement (IRREVERSIBLE)
    if let Err(e) = crate::landlock::confine(policy) {
        fail!(format!("landlock: {}", e));
    }

    // 9. Assemble and install seccomp filter (IRREVERSIBLE)
    let deny = deny_syscall_numbers(policy);
    let args = arg_filters(policy);
    let mut keep_fd: i32 = -1;

    if nested {
        // Nested sandbox: deny-only filter (no supervisor — parent handles it).
        // BPF filters are ANDed by the kernel, so each level can only tighten.
        let filter = bpf::assemble_filter(&[], &deny, &args);
        if let Err(e) = bpf::install_deny_filter(&filter) {
            fail!(format!("seccomp deny filter: {}", e));
        }
        // Signal nested mode to parent (fd=0 means no supervisor needed)
        if let Err(e) = write_u32_fd(pipes.notif_w.as_raw_fd(), 0) {
            fail!(format!("write nested signal: {}", e));
        }
    } else {
        // First-level sandbox: notif + deny filter with NEW_LISTENER.
        let notif = notif_syscalls(policy);
        let filter = bpf::assemble_filter(&notif, &deny, &args);
        let notif_fd = match bpf::install_filter(&filter) {
            Ok(fd) => fd,
            Err(e) => fail!(format!("seccomp install: {}", e)),
        };
        keep_fd = notif_fd.as_raw_fd();
        if let Err(e) = write_u32_fd(pipes.notif_w.as_raw_fd(), keep_fd as u32) {
            fail!(format!("write notif fd: {}", e));
        }
        std::mem::forget(notif_fd);
    }

    // Mark this process as confined for in-process nesting detection
    crate::sandbox::CONFINED.store(true, std::sync::atomic::Ordering::Relaxed);

    // 10. Wait for parent to signal ready
    match read_u32_fd(pipes.ready_r.as_raw_fd()) {
        Ok(_) => {}
        Err(e) => fail!(format!("read ready signal: {}", e)),
    }

    // 12. Optional: close all fds above stderr
    if policy.close_fds {
        if keep_fd >= 0 {
            close_fds_above(2, &[keep_fd]);
        } else {
            close_fds_above(2, &[]);
        }
    }

    // 13. Apply environment
    if policy.clean_env {
        // Clear all env vars first
        for (key, _) in std::env::vars_os() {
            std::env::remove_var(&key);
        }
    }
    for (key, value) in &policy.env {
        std::env::set_var(key, value);
    }

    // 13b. GPU device visibility
    if let Some(ref devices) = policy.gpu_devices {
        if !devices.is_empty() {
            let vis = devices.iter().map(|d| d.to_string()).collect::<Vec<_>>().join(",");
            std::env::set_var("CUDA_VISIBLE_DEVICES", &vis);
            std::env::set_var("ROCR_VISIBLE_DEVICES", &vis);
        }
        // Empty list = all GPUs visible, don't set env vars
    }

    // 14. execvp
    debug_assert!(!cmd.is_empty(), "cmd must not be empty");
    let argv_ptrs: Vec<*const libc::c_char> = cmd
        .iter()
        .map(|s| s.as_ptr())
        .chain(std::iter::once(std::ptr::null()))
        .collect();

    unsafe { libc::execvp(argv_ptrs[0], argv_ptrs.as_ptr()) };

    // If we get here, exec failed
    fail!(format!("execvp '{}'", cmd[0].to_string_lossy()));
}

// ============================================================
// Tests
// ============================================================

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_pipe_pair_creation() {
        let pipes = PipePair::new().expect("pipe creation failed");
        // Verify fds are valid (non-negative)
        assert!(pipes.notif_r.as_raw_fd() >= 0);
        assert!(pipes.notif_w.as_raw_fd() >= 0);
        assert!(pipes.ready_r.as_raw_fd() >= 0);
        assert!(pipes.ready_w.as_raw_fd() >= 0);
        // All four fds should be distinct
        let fds = [
            pipes.notif_r.as_raw_fd(),
            pipes.notif_w.as_raw_fd(),
            pipes.ready_r.as_raw_fd(),
            pipes.ready_w.as_raw_fd(),
        ];
        for i in 0..4 {
            for j in (i + 1)..4 {
                assert_ne!(fds[i], fds[j]);
            }
        }
    }

    #[test]
    fn test_write_read_u32() {
        let pipes = PipePair::new().expect("pipe creation failed");
        let val = 42u32;
        write_u32_fd(pipes.notif_w.as_raw_fd(), val).expect("write failed");
        let got = read_u32_fd(pipes.notif_r.as_raw_fd()).expect("read failed");
        assert_eq!(got, val);
    }

    #[test]
    fn test_write_read_u32_large() {
        let pipes = PipePair::new().expect("pipe creation failed");
        let val = 0xDEAD_BEEFu32;
        write_u32_fd(pipes.notif_w.as_raw_fd(), val).expect("write failed");
        let got = read_u32_fd(pipes.notif_r.as_raw_fd()).expect("read failed");
        assert_eq!(got, val);
    }

    #[test]
    fn test_notif_syscalls_always_has_clone() {
        let policy = Policy::builder().build().unwrap();
        let nrs = notif_syscalls(&policy);
        assert!(nrs.contains(&(libc::SYS_clone as u32)));
        assert!(nrs.contains(&(libc::SYS_clone3 as u32)));
        assert!(nrs.contains(&(libc::SYS_vfork as u32)));
    }

    #[test]
    fn test_notif_syscalls_memory() {
        let policy = Policy::builder()
            .max_memory(crate::policy::ByteSize::mib(256))
            .build()
            .unwrap();
        let nrs = notif_syscalls(&policy);
        assert!(nrs.contains(&(libc::SYS_mmap as u32)));
        assert!(nrs.contains(&(libc::SYS_munmap as u32)));
        assert!(nrs.contains(&(libc::SYS_brk as u32)));
        assert!(nrs.contains(&(libc::SYS_mremap as u32)));
        assert!(nrs.contains(&(libc::SYS_shmget as u32)));
    }

    #[test]
    fn test_notif_syscalls_net() {
        let policy = Policy::builder()
            .net_allow_host("example.com")
            .build()
            .unwrap();
        let nrs = notif_syscalls(&policy);
        assert!(nrs.contains(&(libc::SYS_connect as u32)));
        assert!(nrs.contains(&(libc::SYS_sendto as u32)));
        assert!(nrs.contains(&(libc::SYS_sendmsg as u32)));
    }

    #[test]
    fn test_deny_syscall_numbers_default() {
        let policy = Policy::builder().build().unwrap();
        let nrs = deny_syscall_numbers(&policy);
        // Should contain mount, ptrace, etc.
        assert!(nrs.contains(&(libc::SYS_mount as u32)));
        assert!(nrs.contains(&(libc::SYS_ptrace as u32)));
        assert!(nrs.contains(&(libc::SYS_bpf as u32)));
        // nfsservctl has no libc constant, so it is skipped
        assert!(!nrs.is_empty());
    }

    #[test]
    fn test_deny_syscall_numbers_custom() {
        let policy = Policy::builder()
            .deny_syscalls(vec!["mount".into(), "ptrace".into()])
            .build()
            .unwrap();
        let nrs = deny_syscall_numbers(&policy);
        assert_eq!(nrs.len(), 2);
        assert!(nrs.contains(&(libc::SYS_mount as u32)));
        assert!(nrs.contains(&(libc::SYS_ptrace as u32)));
    }

    #[test]
    fn test_deny_syscall_numbers_empty_when_allow_set() {
        let policy = Policy::builder()
            .allow_syscalls(vec!["read".into(), "write".into()])
            .build()
            .unwrap();
        let nrs = deny_syscall_numbers(&policy);
        assert!(nrs.is_empty());
    }

    #[test]
    fn test_arg_filters_has_clone_ioctl_prctl_socket() {
        use crate::sys::structs::{
            BPF_JEQ, BPF_JSET, BPF_JMP, BPF_K,
        };
        let policy = Policy::builder().build().unwrap();
        let filters = arg_filters(&policy);
        // Should contain JEQ for clone syscall nr
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == libc::SYS_clone as u32));
        // Should contain JSET for CLONE_NS_FLAGS
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JSET | BPF_K)
            && f.k == CLONE_NS_FLAGS as u32));
        // Should contain JEQ for ioctl syscall nr
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == libc::SYS_ioctl as u32));
        // Should contain JEQ for TIOCSTI and TIOCLINUX
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == TIOCSTI as u32));
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == TIOCLINUX as u32));
        // Should contain JEQ for prctl syscall nr
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == libc::SYS_prctl as u32));
        // Should contain JEQ for PR_SET_DUMPABLE
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == PR_SET_DUMPABLE));
        // Should contain JEQ for socket + AF_NETLINK + NETLINK_SOCK_DIAG
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == AF_NETLINK));
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == NETLINK_SOCK_DIAG));
    }

    #[test]
    fn test_arg_filters_raw_sockets() {
        use crate::sys::structs::{BPF_ALU, BPF_AND, BPF_JEQ, BPF_JMP, BPF_K};
        let policy = Policy::builder().no_raw_sockets(true).build().unwrap();
        let filters = arg_filters(&policy);
        // Should have AF_INET check
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == AF_INET));
        // Should have AF_INET6 check
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == AF_INET6));
        // Should have ALU AND SOCK_TYPE_MASK
        assert!(filters.iter().any(|f| f.code == (BPF_ALU | BPF_AND | BPF_K)
            && f.k == SOCK_TYPE_MASK));
        // Should have JEQ SOCK_RAW
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == SOCK_RAW));
    }

    #[test]
    fn test_arg_filters_no_udp() {
        use crate::sys::structs::{BPF_JEQ, BPF_JMP, BPF_K};
        let policy = Policy::builder().no_udp(true).build().unwrap();
        let filters = arg_filters(&policy);
        // Should have JEQ SOCK_DGRAM
        assert!(filters.iter().any(|f| f.code == (BPF_JMP | BPF_JEQ | BPF_K)
            && f.k == SOCK_DGRAM));
    }

    #[test]
    fn test_syscall_name_to_nr_covers_defaults() {
        // Every name in DEFAULT_DENY_SYSCALLS except nfsservctl should resolve
        let mut skipped = 0;
        for name in DEFAULT_DENY_SYSCALLS {
            match syscall_name_to_nr(name) {
                Some(_) => {}
                None => {
                    assert_eq!(*name, "nfsservctl", "unexpected unresolved syscall: {}", name);
                    skipped += 1;
                }
            }
        }
        assert_eq!(skipped, 1); // only nfsservctl
    }
}