ceamac
9877ffe7f1
Long-option only. Threaded through run_container() into build_bwrap_args(), which passes it as bwrap's own --hostname only when --unshare-uts is actually among the flags being given to bwrap (bwrap itself refuses --hostname without it) -- otherwise logs a warning and leaves the hostname alone, since a stock Android kernel in degraded mode may not support a UTS namespace at all. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Gv3s5jckJKzh6JkMoi2Akz
83 lines
4.7 KiB
C++
83 lines
4.7 KiB
C++
// Copyright (C) 2026 Viorel Munteanu
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//
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// This program is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 2 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License along
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// with this program; if not, write to the Free Software Foundation, Inc.,
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// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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#pragma once
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#include <optional>
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#include <string>
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#include <vector>
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#include "volume_mount.h"
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// Probes the running kernel for which Linux namespace types can actually be
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// unshared and returns the corresponding bwrap --unshare-xxx flags for the
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// ones that are supported. Intended for kernels with partial namespace
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// support (e.g. stock Android kernels), where blindly passing every
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// --unshare-xxx flag to bwrap would make it fail outright.
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std::vector<std::string> detect_bwrap_unshare_args();
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// Wraps `argv` so it runs inside the mount+user namespace that containers-storage's
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// rootless fuse-overlayfs daemon created for `root` (the merged mount path from
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// mount_layer()), via nsenter -- needed to reach anything under `root` at all from a
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// plain process outside that namespace (containers-storage mount reexecs itself
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// into a private namespace to get the privilege an unprivileged overlay mount
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// needs; only nsenter targeting that live daemon's PID can rejoin it). If
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// use_nsenter is false, returns argv unchanged (the mount is already directly
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// visible, e.g. when running as root -- see run_container() in main.cpp). Returns
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// nullopt (and logs) if the fuse-overlayfs process or nsenter itself can't be
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// found.
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std::optional<std::vector<std::string>> wrap_for_root_namespace(const std::string& root, bool use_nsenter,
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const std::vector<std::string>& argv);
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struct ResolvedUser {
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int uid;
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int gid;
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std::string home; // from the image's /etc/passwd entry for uid, or a sane fallback
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};
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// Assembles the full bwrap argv (program name included) to run `command` with
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// `root` bound as the sandbox's filesystem root, using whichever --unshare-xxx
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// flags the kernel supports (see detect_bwrap_unshare_args()). Each entry in
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// `volumes` is bound writably at its container_path (see resolve_volume_mount()
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// in volume_mount.h). If `user` is set, the command is wrapped so it drops to that
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// uid/gid before running -- see run_bwrap() for how, since bwrap's own --uid/--gid
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// require --unshare-user, which isn't requested when running as root (see
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// detect_bwrap_unshare_args()). If `hostname` is set and the kernel supports
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// --unshare-uts (bwrap refuses --hostname without it), passes it as bwrap's own
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// --hostname; otherwise logs a warning and leaves the sandbox's hostname alone.
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std::vector<std::string> build_bwrap_args(const std::string& root,
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const std::vector<std::string>& command,
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const std::vector<ResolvedVolumeMount>& volumes,
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std::optional<ResolvedUser> user,
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const std::optional<std::string>& hostname);
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// Runs bwrap against `root` (the merged mount path from mount_layer()) in the
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// foreground and waits for it to exit. If `use_nsenter` is true, first locates the
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// fuse-overlayfs process serving `root` and runs bwrap via nsenter into that
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// process's user+mount namespaces -- needed because containers-storage mount
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// (rootless) creates the overlay mount inside a private namespace invisible to a
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// plain child process on kernels where fuse-overlayfs isolates it that way. Pass
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// use_nsenter=false on kernels where the mount is already directly visible
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// (observed on kernels older than 4.18, per fuse-overlayfs's own release notes).
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// If `user` is set, this process's own binary is bind-mounted into the sandbox and
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// used to drop privileges to that uid/gid before running `command` -- see
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// build_bwrap_args(). `hostname`, if set, is forwarded to build_bwrap_args() --
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// see there for when it does/doesn't take effect. Returns bwrap's exit code, or -1
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// on failure to launch.
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int run_bwrap(const std::string& root, const std::vector<std::string>& command, bool use_nsenter,
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const std::vector<ResolvedVolumeMount>& volumes, std::optional<ResolvedUser> user,
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const std::optional<std::string>& hostname);
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