slocker-lite/tests/integration/test_session_cleanup.cpp

// Copyright (C) 2026 Viorel Munteanu
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License along
// with this program; if not, write to the Free Software Foundation, Inc.,
// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

// [integration][root]: regression test for run_bwrap()'s own automatic
// post-exit straggler sweep (bwrap.cpp) -- exercises the exported
// kill_via_cgroup() (kill_session.h) directly against a real cgroup, rather
// than going through the full mount/bwrap pipeline. That's a deliberate
// choice, not a shortcut: the actual bug this targets is a process that
// daemonizes/double-forks and setsid()'s away, reparenting outside the
// tracked process's own tree (e.g. no pid namespace support at all, the
// real target device's own kernel) -- reproducing that specific escape
// through a real bwrap sandbox would need to fake the kernel's own pid
// namespace absence (not controllable from the CLI at all -- it's a
// config-file-only NamespaceConfig field, see bwrap.h), whereas the actual
// mechanism under test (cgroup membership surviving reparenting, and
// kill_via_cgroup() reaping it) is fully exercised with two plain forked
// processes and no container/image/bwrap involved at all.

#include <unistd.h>

#include <csignal>
#include <string>

#include <sys/wait.h>

#include <catch2/catch_test_macros.hpp>

#include "kill_session.h"
#include "session_cgroup.h"

TEST_CASE("session cgroup sweep: kill_via_cgroup reaps a reparented straggler", "[integration][root]") {
    if (geteuid() != 0) {
        SKIP("requires root");
    }

    const std::string container_name = "test-cgroup-sweep";

    // sync_pipe makes the child wait until it's actually been moved into the
    // session cgroup before it forks its own straggler -- otherwise the
    // straggler could be forked (and thus inherit cgroup membership) before
    // create_session_cgroup() below has run, racing the exact same way
    // run_bwrap()'s own on_start callback races against bwrap forking its
    // own children.
    int sync_pipe[2];
    REQUIRE(pipe(sync_pipe) == 0);

    pid_t tracked_pid = fork();
    REQUIRE(tracked_pid >= 0);
    if (tracked_pid == 0) {
        close(sync_pipe[1]);
        char buf = 0;
        ssize_t unused = read(sync_pipe[0], &buf, 1);
        (void)unused;
        close(sync_pipe[0]);

        // Reset to the default disposition before forking: the straggler
        // below is expected to receive a real SIGTERM later (from
        // kill_via_cgroup()) and terminate via it -- Catch2 installs its own
        // fatal-signal handler around a running TEST_CASE, which a forked
        // child inherits (only the disposition *at fork time* matters), so
        // without this reset the straggler's own ordinary shutdown signal
        // gets caught by that inherited handler instead, producing a
        // spurious "FAILED ... due to a fatal error condition: SIGTERM"
        // report interleaved into this test's real output -- the exact same
        // lesson test_root_networking.cpp's tap-relay test already learned
        // for its own forked relay child. Confirmed cosmetic only when hit:
        // the assertions below still ran and passed correctly either way.
        signal(SIGTERM, SIG_DFL);

        // Mirrors a container process that daemonizes and exits successfully
        // (or is signaled and dies) while a backgrounded child of its own
        // keeps running, detached into a new session -- the exact shape
        // that used to escape bwrap's own pid tree with nothing left to
        // reap it.
        pid_t straggler = fork();
        if (straggler == 0) {
            setsid();
            pause();
            _exit(0);
        }
        _exit(0);
    }
    close(sync_pipe[0]);

    // Mirrors create_session_cgroup() being called from run_bwrap()'s own
    // on_start callback, the instant the tracked pid is known -- before it's
    // had any real chance to fork further.
    auto cgroup = create_session_cgroup(container_name, tracked_pid);
    if (!cgroup) {
        char go = 1;
        ssize_t unused = write(sync_pipe[1], &go, 1);
        (void)unused;
        close(sync_pipe[1]);
        int status = 0;
        waitpid(tracked_pid, &status, 0);
        SKIP("could not create a session cgroup on this host (see session_cgroup.h)");
    }

    char go = 1;
    REQUIRE(write(sync_pipe[1], &go, 1) == 1);
    close(sync_pipe[1]);

    int status = 0;
    // Mirrors run_process_foreground()'s own waitpid() on the tracked pid --
    // by the time this returns, `tracked_pid` is already gone from
    // cgroup.procs (a dead process is removed from its cgroup
    // automatically), leaving only the straggler behind, exactly like a
    // real bwrap exit would.
    waitpid(tracked_pid, &status, 0);

    auto before = session_cgroup_pids(*cgroup);
    // Confirms the straggler really did escape into the cgroup in the first
    // place -- otherwise the kill_via_cgroup() check below would trivially
    // "pass" against an already-empty cgroup and prove nothing.
    REQUIRE_FALSE(before.empty());

    CHECK(kill_via_cgroup(*cgroup, /*grace_period_seconds=*/2));
    CHECK(session_cgroup_pids(*cgroup).empty());

    remove_session_cgroup(*cgroup);
}