#include "command.hh" #include "common-args.hh" #include "shared.hh" #include "store-api.hh" #include "derivations.hh" #include "local-store.hh" #include "finally.hh" #include "fs-accessor.hh" #include "progress-bar.hh" #if __linux__ #include <sys/mount.h> #endif using namespace nix; std::string chrootHelperName = "__run_in_chroot"; extern char * * environ; struct CmdRun : InstallablesCommand { Strings command = { "bash" }; StringSet keep, unset; bool ignoreEnvironment = false; CmdRun() { mkFlag() .longName("command") .shortName('c') .description("command and arguments to be executed; defaults to 'bash'") .arity(ArityAny) .labels({"command", "args"}) .handler([&](Strings ss) { if (ss.empty()) throw UsageError("--command requires at least one argument"); command = ss; }); mkFlag() .longName("ignore-environment") .shortName('i') .description("clear the entire environment (except those specified with --keep)") .set(&ignoreEnvironment, true); mkFlag() .longName("keep") .shortName('k') .description("keep specified environment variable") .arity(1) .labels({"name"}) .handler([&](Strings ss) { keep.insert(ss.front()); }); mkFlag() .longName("unset") .shortName('u') .description("unset specified environment variable") .arity(1) .labels({"name"}) .handler([&](Strings ss) { unset.insert(ss.front()); }); } std::string name() override { return "run"; } std::string description() override { return "run a shell in which the specified packages are available"; } Examples examples() override { return { Example{ "To start a shell providing GNU Hello from NixOS 17.03:", "nix run -f channel:nixos-17.03 hello" }, Example{ "To start a shell providing youtube-dl from your 'nixpkgs' channel:", "nix run nixpkgs.youtube-dl" }, Example{ "To run GNU Hello:", "nix run nixpkgs.hello -c hello --greeting 'Hi everybody!'" }, }; } void run(ref<Store> store) override { auto outPaths = toStorePaths(store, Build); auto accessor = store->getFSAccessor(); if (ignoreEnvironment) { if (!unset.empty()) throw UsageError("--unset does not make sense with --ignore-environment"); std::map<std::string, std::string> kept; for (auto & var : keep) { auto s = getenv(var.c_str()); if (s) kept[var] = s; } environ = nullptr; for (auto & var : kept) setenv(var.first.c_str(), var.second.c_str(), 1); } else { if (!keep.empty()) throw UsageError("--keep does not make sense without --ignore-environment"); for (auto & var : unset) unsetenv(var.c_str()); } auto unixPath = tokenizeString<Strings>(getEnv("PATH"), ":"); for (auto & path : outPaths) if (accessor->stat(path + "/bin").type != FSAccessor::tMissing) unixPath.push_front(path + "/bin"); setenv("PATH", concatStringsSep(":", unixPath).c_str(), 1); std::string cmd = *command.begin(); Strings args = command; stopProgressBar(); /* If this is a diverted store (i.e. its "logical" location (typically /nix/store) differs from its "physical" location (e.g. /home/eelco/nix/store), then run the command in a chroot. For non-root users, this requires running it in new mount and user namespaces. Unfortunately, unshare(CLONE_NEWUSER) doesn't work in a multithreaded program (which "nix" is), so we exec() a single-threaded helper program (chrootHelper() below) to do the work. */ auto store2 = store.dynamic_pointer_cast<LocalStore>(); if (store2 && store->storeDir != store2->realStoreDir) { Strings helperArgs = { chrootHelperName, store->storeDir, store2->realStoreDir, cmd }; for (auto & arg : args) helperArgs.push_back(arg); execv(readLink("/proc/self/exe").c_str(), stringsToCharPtrs(helperArgs).data()); throw SysError("could not execute chroot helper"); } execvp(cmd.c_str(), stringsToCharPtrs(args).data()); throw SysError("unable to exec '%s'", cmd); } }; static RegisterCommand r1(make_ref<CmdRun>()); void chrootHelper(int argc, char * * argv) { int p = 1; std::string storeDir = argv[p++]; std::string realStoreDir = argv[p++]; std::string cmd = argv[p++]; Strings args; while (p < argc) args.push_back(argv[p++]); #if __linux__ uid_t uid = getuid(); uid_t gid = getgid(); if (unshare(CLONE_NEWUSER | CLONE_NEWNS) == -1) throw SysError("setting up a private mount namespace"); /* Bind-mount realStoreDir on /nix/store. If the latter mount point doesn't already exists, we have to create a chroot environment containing the mount point and bind mounts for the children of /. Would be nice if we could use overlayfs here, but that doesn't work in a user namespace yet (Ubuntu has a patch for this: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1478578). */ if (true /* !pathExists(storeDir) */) { // FIXME: Use overlayfs? Path tmpDir = createTempDir(); createDirs(tmpDir + storeDir); if (mount(realStoreDir.c_str(), (tmpDir + storeDir).c_str(), "", MS_BIND, 0) == -1) throw SysError("mounting '%s' on '%s'", realStoreDir, storeDir); for (auto entry : readDirectory("/")) { Path dst = tmpDir + "/" + entry.name; if (pathExists(dst)) continue; if (mkdir(dst.c_str(), 0700) == -1) throw SysError(format("creating directory '%s'") % dst); if (mount(("/" + entry.name).c_str(), dst.c_str(), "", MS_BIND | MS_REC, 0) == -1) throw SysError(format("mounting '%s' on '%s'") % ("/" + entry.name) % dst); } char * cwd = getcwd(0, 0); if (!cwd) throw SysError("getting current directory"); Finally freeCwd([&]() { free(cwd); }); if (chroot(tmpDir.c_str()) == -1) throw SysError(format("chrooting into '%s'") % tmpDir); if (chdir(cwd) == -1) throw SysError(format("chdir to '%s' in chroot") % cwd); } else if (mount(realStoreDir.c_str(), storeDir.c_str(), "", MS_BIND, 0) == -1) throw SysError("mounting '%s' on '%s'", realStoreDir, storeDir); writeFile("/proc/self/setgroups", "deny"); writeFile("/proc/self/uid_map", fmt("%d %d %d", uid, uid, 1)); writeFile("/proc/self/gid_map", fmt("%d %d %d", gid, gid, 1)); execvp(cmd.c_str(), stringsToCharPtrs(args).data()); throw SysError("unable to exec '%s'", cmd); #else throw Error("mounting the Nix store on '%s' is not supported on this platform", storeDir); #endif }