1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139

#include "c-calls.hh"
#include "lix/libutil/file-descriptor.hh"
#include "lix/libutil/file-system.hh"
#include "lix/libutil/logging.hh"
#include "lix/libutil/namespaces.hh"
#include "lix/libutil/processes.hh"
#include "lix/libutil/strings.hh"

#include <kj/common.h>
#include <ranges>
#include <sys/mount.h>

#if __linux__
# include <mutex>
# include <sys/resource.h>
#endif

namespace nix {

#if __linux__
static AutoCloseFD fdSavedMountNamespace;
static AutoCloseFD fdSavedRoot;
#endif

void saveMountNamespace()
{
#if __linux__
    static std::once_flag done;
    std::call_once(done, []() {
        fdSavedMountNamespace = AutoCloseFD{open("/proc/self/ns/mnt", O_RDONLY)};
        if (!fdSavedMountNamespace)
            throw SysError("saving parent mount namespace");

        fdSavedRoot = AutoCloseFD{open("/proc/self/root", O_RDONLY)};
    });
#endif
}

void restoreMountNamespace()
{
#if __linux__
    try {
        auto savedCwd = absPath(".");

        if (fdSavedMountNamespace && setns(fdSavedMountNamespace.get(), CLONE_NEWNS) == -1)
            throw SysError("restoring parent mount namespace");

        if (fdSavedRoot) {
            if (fchdir(fdSavedRoot.get()))
                throw SysError("chdir into saved root");
            if (chroot("."))
                throw SysError("chroot into saved root");
        }

        if (sys::chdir(savedCwd) == -1) {
            throw SysError("restoring cwd");
        }
    } catch (Error & e) {
        debug("%1%", Uncolored(e.msg()));
    }
#endif
}

void unshareFilesystem()
{
#ifdef __linux__
    if (unshare(CLONE_FS) != 0 && errno != EPERM)
        throw SysError("unsharing filesystem state in download thread");
#endif
}


#if __linux__

static void diagnoseUserNamespaces()
{
    if (!pathExists("/proc/self/ns/user")) {
        printTaggedWarning(
            "'/proc/self/ns/user' does not exist; your kernel was likely built without "
            "CONFIG_USER_NS=y"
        );
    }

    Path maxUserNamespaces = "/proc/sys/user/max_user_namespaces";
    if (!pathExists(maxUserNamespaces) ||
        trim(readFile(maxUserNamespaces)) == "0")
    {
        printTaggedWarning(
            "user namespaces appear to be disabled; check '/proc/sys/user/max_user_namespaces'"
        );
    }

    Path procSysKernelUnprivilegedUsernsClone = "/proc/sys/kernel/unprivileged_userns_clone";
    if (pathExists(procSysKernelUnprivilegedUsernsClone)
        && trim(readFile(procSysKernelUnprivilegedUsernsClone)) == "0")
    {
        printTaggedWarning(
            "user namespaces appear to be disabled for unprivileged users; check "
            "'/proc/sys/kernel/unprivileged_userns_clone'"
        );
    }
}

kj::Promise<Result<AvailableNamespaces>> queryAvailableNamespaces()
try {
    AvailableNamespaces result{};

    auto helper = runHelper("check-namespace-support", {.captureStdout = true});
    KJ_DEFER(helper.waitAndCheck());
    const auto results = tokenizeString<Strings>(TRY_AWAIT(helper.getStdout()->drain()), "\n");

    for (auto line : results) {
        if (line == "user") {
            result.user = true;
        } else if (line.starts_with("user ")) {
            printTaggedWarning("user namespaces do not work on this system: %s", line.substr(5));
            diagnoseUserNamespaces();
        } else if (line == "mount-pid") {
            result.mountAndPid = true;
        } else if (line.starts_with("mount-pid")) {
            debug("mount namespaces do not work on this system: %s", line.substr(9));
        } else {
            throw Error("unexpected namespace check status: %s", line);
        }
    }

    co_return result;
} catch (...) {
    co_return result::current_exception();
}
#else
kj::Promise<Result<AvailableNamespaces>> queryAvailableNamespaces()
try {
    return {AvailableNamespaces{}};
} catch (...) {
    return {result::current_exception()};
}
#endif
}