153 lines
4.0 KiB
C++
153 lines
4.0 KiB
C++
#include "file-descriptor.hh"
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#include "file-system.hh"
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#include "logging.hh"
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#include "namespaces.hh"
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#include "processes.hh"
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#include "strings.hh"
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#include <sys/mount.h>
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#if __linux__
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# include <mutex>
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# include <sys/resource.h>
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#endif
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namespace nix {
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#if __linux__
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static AutoCloseFD fdSavedMountNamespace;
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static AutoCloseFD fdSavedRoot;
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#endif
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void saveMountNamespace()
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{
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#if __linux__
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static std::once_flag done;
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std::call_once(done, []() {
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fdSavedMountNamespace = AutoCloseFD{open("/proc/self/ns/mnt", O_RDONLY)};
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if (!fdSavedMountNamespace)
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throw SysError("saving parent mount namespace");
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fdSavedRoot = AutoCloseFD{open("/proc/self/root", O_RDONLY)};
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});
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#endif
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}
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void restoreMountNamespace()
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{
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#if __linux__
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try {
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auto savedCwd = absPath(".");
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if (fdSavedMountNamespace && setns(fdSavedMountNamespace.get(), CLONE_NEWNS) == -1)
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throw SysError("restoring parent mount namespace");
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if (fdSavedRoot) {
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if (fchdir(fdSavedRoot.get()))
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throw SysError("chdir into saved root");
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if (chroot("."))
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throw SysError("chroot into saved root");
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}
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if (chdir(savedCwd.c_str()) == -1)
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throw SysError("restoring cwd");
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} catch (Error & e) {
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debug(e.msg());
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}
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#endif
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}
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void unshareFilesystem()
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{
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#ifdef __linux__
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if (unshare(CLONE_FS) != 0 && errno != EPERM)
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throw SysError("unsharing filesystem state in download thread");
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#endif
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}
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#if __linux__
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static void diagnoseUserNamespaces()
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{
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if (!pathExists("/proc/self/ns/user")) {
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warn("'/proc/self/ns/user' does not exist; your kernel was likely built without CONFIG_USER_NS=y");
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}
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Path maxUserNamespaces = "/proc/sys/user/max_user_namespaces";
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if (!pathExists(maxUserNamespaces) ||
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trim(readFile(maxUserNamespaces)) == "0")
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{
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warn("user namespaces appear to be disabled; check '/proc/sys/user/max_user_namespaces'");
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}
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Path procSysKernelUnprivilegedUsernsClone = "/proc/sys/kernel/unprivileged_userns_clone";
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if (pathExists(procSysKernelUnprivilegedUsernsClone)
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&& trim(readFile(procSysKernelUnprivilegedUsernsClone)) == "0")
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{
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warn("user namespaces appear to be disabled for unprivileged users; check '/proc/sys/kernel/unprivileged_userns_clone'");
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}
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}
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bool userNamespacesSupported()
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{
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static auto res = [&]() -> bool
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{
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try {
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Pid pid = startProcess([&]() { _exit(0); }, {.cloneFlags = CLONE_NEWUSER});
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auto r = pid.wait();
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assert(!r);
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} catch (SysError & e) {
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warn("user namespaces do not work on this system: %s", e.msg());
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diagnoseUserNamespaces();
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return false;
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}
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return true;
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}();
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return res;
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}
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bool mountAndPidNamespacesSupported()
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{
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static auto res = [&]() -> bool
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{
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try {
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Pid pid = startProcess([&]() {
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/* Make sure we don't remount the parent's /proc. */
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if (mount(0, "/", 0, MS_PRIVATE | MS_REC, 0) == -1)
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_exit(1);
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/* Test whether we can remount /proc. The kernel disallows
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this if /proc is not fully visible, i.e. if there are
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filesystems mounted on top of files inside /proc. See
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https://lore.kernel.org/lkml/87tvsrjai0.fsf@xmission.com/T/. */
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if (mount("none", "/proc", "proc", 0, 0) == -1)
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_exit(2);
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_exit(0);
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}, {
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.cloneFlags = CLONE_NEWNS | CLONE_NEWPID | (userNamespacesSupported() ? CLONE_NEWUSER : 0)
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});
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if (pid.wait()) {
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debug("PID namespaces do not work on this system: cannot remount /proc");
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return false;
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}
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} catch (SysError & e) {
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debug("mount namespaces do not work on this system: %s", e.msg());
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return false;
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}
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return true;
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}();
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return res;
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}
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#endif
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}
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