diff options
Diffstat (limited to 'src/nix')
| -rw-r--r-- | src/nix/main.cc | 11 | ||||
| -rw-r--r-- | src/nix/run.cc | 159 |
2 files changed, 110 insertions, 60 deletions
diff --git a/src/nix/main.cc b/src/nix/main.cc index 7fece5b87b0b..0990549aeecd 100644 --- a/src/nix/main.cc +++ b/src/nix/main.cc @@ -9,6 +9,10 @@ #include "store-api.hh" #include "progress-bar.hh" +extern std::string chrootHelperName; + +void chrootHelper(int argc, char * * argv); + namespace nix { struct NixArgs : virtual MultiCommand, virtual MixCommonArgs @@ -57,6 +61,13 @@ void mainWrapped(int argc, char * * argv) verbosity = lvlError; settings.verboseBuild = false; + /* The chroot helper needs to be run before any threads have been + started. */ + if (argc > 0 && argv[0] == chrootHelperName) { + chrootHelper(argc, argv); + return; + } + initNix(); initGC(); diff --git a/src/nix/run.cc b/src/nix/run.cc index f67fd637c4fa..e58e2f187a2d 100644 --- a/src/nix/run.cc +++ b/src/nix/run.cc @@ -5,6 +5,7 @@ #include "derivations.hh" #include "local-store.hh" #include "finally.hh" +#include "fs-accessor.hh" #if __linux__ #include <sys/mount.h> @@ -12,6 +13,8 @@ using namespace nix; +std::string chrootHelperName = "__run_in_chroot"; + struct CmdRun : InstallablesCommand { CmdRun() @@ -32,73 +35,109 @@ struct CmdRun : InstallablesCommand { auto outPaths = toStorePaths(store, Build); - auto store2 = store.dynamic_pointer_cast<LocalStore>(); - - if (store2 && store->storeDir != store2->realStoreDir) { -#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 (!pathExists(store->storeDir)) { - // FIXME: Use overlayfs? - - Path tmpDir = createTempDir(); - - createDirs(tmpDir + store->storeDir); - - if (mount(store2->realStoreDir.c_str(), (tmpDir + store->storeDir).c_str(), "", MS_BIND, 0) == -1) - throw SysError(format("mounting '%s' on '%s'") % store2->realStoreDir % store->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(store2->realStoreDir.c_str(), store->storeDir.c_str(), "", MS_BIND, 0) == -1) - throw SysError(format("mounting '%s' on '%s'") % store2->realStoreDir % store->storeDir); - - writeFile("/proc/self/setgroups", "deny"); - writeFile("/proc/self/uid_map", (format("%d %d %d") % uid % uid % 1).str()); - writeFile("/proc/self/gid_map", (format("%d %d %d") % gid % gid % 1).str()); -#else - throw Error(format("mounting the Nix store on '%s' is not supported on this platform") % store->storeDir); -#endif - } - + auto accessor = store->getFSAccessor(); auto unixPath = tokenizeString<Strings>(getEnv("PATH"), ":"); for (auto & path : outPaths) - if (pathExists(path + "/bin")) + if (accessor->stat(path + "/bin").type != FSAccessor::tMissing) unixPath.push_front(path + "/bin"); setenv("PATH", concatStringsSep(":", unixPath).c_str(), 1); - if (execlp("bash", "bash", nullptr) == -1) - throw SysError("unable to exec 'bash'"); + std::string cmd = "bash"; + Strings args = { cmd }; + + /* 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 +} |