diff options
| -rw-r--r-- | Makefile.config.in | 1 | ||||
| -rw-r--r-- | configure.ac | 9 | ||||
| -rw-r--r-- | release.nix | 7 | ||||
| -rw-r--r-- | src/libstore/build.cc | 94 | ||||
| -rw-r--r-- | src/libstore/local.mk | 4 | ||||
| -rw-r--r-- | tests/sandbox.nix | 54 |
6 files changed, 139 insertions, 30 deletions
diff --git a/Makefile.config.in b/Makefile.config.in index a03776d57..08408ea5f 100644 --- a/Makefile.config.in +++ b/Makefile.config.in @@ -10,6 +10,7 @@ OPENSSL_LIBS = @OPENSSL_LIBS@ PACKAGE_NAME = @PACKAGE_NAME@ PACKAGE_VERSION = @PACKAGE_VERSION@ SODIUM_LIBS = @SODIUM_LIBS@ +LIBSECCOMP_LIBS = @LIBSECCOMP_LIBS@ LIBLZMA_LIBS = @LIBLZMA_LIBS@ SQLITE3_LIBS = @SQLITE3_LIBS@ bash = @bash@ diff --git a/configure.ac b/configure.ac index e6b11be2d..4e1806270 100644 --- a/configure.ac +++ b/configure.ac @@ -193,6 +193,15 @@ AC_SUBST(HAVE_SODIUM, [$have_sodium]) PKG_CHECK_MODULES([LIBLZMA], [liblzma], [CXXFLAGS="$LIBLZMA_CFLAGS $CXXFLAGS"]) +# Look for libseccomp, required for Linux sandboxing. +if test "$sys_name" = linux; then + PKG_CHECK_MODULES([LIBSECCOMP], [libseccomp], + [CXXFLAGS="$LIBSECCOMP_CFLAGS $CXXFLAGS"]) +# AC_CHECK_LIB([seccomp], [seccomp_init], [true], +# [AC_MSG_ERROR([Nix requires libseccomp for sandboxing. See https://github.com/seccomp/libseccomp.])]) +fi + + # Look for aws-cpp-sdk-s3. AC_LANG_PUSH(C++) AC_CHECK_HEADERS([aws/s3/S3Client.h], diff --git a/release.nix b/release.nix index d825dd583..7c5e6125b 100644 --- a/release.nix +++ b/release.nix @@ -25,7 +25,7 @@ let buildInputs = [ curl bison flex perl libxml2 libxslt bzip2 xz - pkgconfig sqlite libsodium boehmgc + pkgconfig sqlite libsodium libseccomp boehmgc docbook5 docbook5_xsl autoconf-archive ] ++ lib.optional (!lib.inNixShell) git; @@ -74,6 +74,7 @@ let buildInputs = [ curl perl bzip2 xz openssl pkgconfig sqlite boehmgc ] ++ lib.optional stdenv.isLinux libsodium + ++ lib.optional stdenv.isLinux libseccomp ++ lib.optional stdenv.isLinux (aws-sdk-cpp.override { apis = ["s3"]; @@ -196,6 +197,10 @@ let nix = build.x86_64-linux; system = "x86_64-linux"; }); + tests.sandbox = (import ./tests/sandbox.nix rec { + nix = build.x86_64-linux; system = "x86_64-linux"; + }); + tests.binaryTarball = with import <nixpkgs> { system = "x86_64-linux"; }; vmTools.runInLinuxImage (runCommand "nix-binary-tarball-test" diff --git a/src/libstore/build.cc b/src/libstore/build.cc index c970fbdca..f702433a0 100644 --- a/src/libstore/build.cc +++ b/src/libstore/build.cc @@ -54,6 +54,7 @@ #include <sys/param.h> #include <sys/mount.h> #include <sys/syscall.h> +#include <seccomp.h> #define pivot_root(new_root, put_old) (syscall(SYS_pivot_root, new_root, put_old)) #endif @@ -814,9 +815,6 @@ private: result. */ ValidPathInfos prevInfos; - const uid_t sandboxUid = 1000; - const gid_t sandboxGid = 100; - public: DerivationGoal(const Path & drvPath, const StringSet & wantedOutputs, Worker & worker, BuildMode buildMode = bmNormal); @@ -1644,8 +1642,56 @@ void chmod_(const Path & path, mode_t mode) } +#if __linux__ + +#define FORCE_SUCCESS(syscall) \ + if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(0), SCMP_SYS(syscall), 0) != 0) { \ + seccomp_release(ctx); \ + throw SysError("unable to add seccomp rule for " #syscall); \ + } + +void setupSeccomp(void) { + scmp_filter_ctx ctx; + + if ((ctx = seccomp_init(SCMP_ACT_ALLOW)) == NULL) + throw SysError("unable to initialize seccomp mode 2"); + +#if defined(__x86_64__) + if (seccomp_arch_add(ctx, SCMP_ARCH_X86) != 0) { + seccomp_release(ctx); + throw SysError("unable to add 32bit seccomp architecture"); + } +#endif + + FORCE_SUCCESS(chown32); + FORCE_SUCCESS(fchown32); + FORCE_SUCCESS(lchown32); + + FORCE_SUCCESS(chown); + FORCE_SUCCESS(fchown); + FORCE_SUCCESS(fchownat); + FORCE_SUCCESS(lchown); + + FORCE_SUCCESS(setxattr); + FORCE_SUCCESS(lsetxattr); + FORCE_SUCCESS(fsetxattr); + + if (seccomp_load(ctx) != 0) { + seccomp_release(ctx); + throw SysError("unable to load seccomp BPF program"); + } + + seccomp_release(ctx); +} + +#undef FORCE_SUCCESS + +#endif + + int childEntry(void * arg) { + setupSeccomp(); ((DerivationGoal *) arg)->runChild(); return 1; } @@ -1965,18 +2011,14 @@ void DerivationGoal::startBuilder() createDirs(chrootRootDir + "/etc"); writeFile(chrootRootDir + "/etc/passwd", - (format( - "root:x:0:0:Nix build user:/:/noshell\n" - "nixbld:x:%1%:%2%:Nix build user:/:/noshell\n" - "nobody:x:65534:65534:Nobody:/:/noshell\n") % sandboxUid % sandboxGid).str()); + "root:x:0:0:Nix build user:/:/noshell\n" + "nobody:x:65534:65534:Nobody:/:/noshell\n"); /* Declare the build user's group so that programs get a consistent view of the system (e.g., "id -gn"). */ writeFile(chrootRootDir + "/etc/group", - (format( - "root:x:0:\n" - "nixbld:!:%1%:\n" - "nogroup:x:65534:\n") % sandboxGid).str()); + "root:x:0:\n" + "nobody:x:65534:\n"); /* Create /etc/hosts with localhost entry. */ if (!fixedOutput) @@ -2160,12 +2202,7 @@ void DerivationGoal::startBuilder() Pid helper = startProcess([&]() { /* Drop additional groups here because we can't do it - after we've created the new user namespace. FIXME: - this means that if we're not root in the parent - namespace, we can't drop additional groups; they will - be mapped to nogroup in the child namespace. There does - not seem to be a workaround for this. (But who can tell - from reading user_namespaces(7)?)*/ + after we've created the new user namespace. */ if (getuid() == 0 && setgroups(0, 0) == -1) throw SysError("setgroups failed"); @@ -2198,19 +2235,19 @@ void DerivationGoal::startBuilder() if (!string2Int<pid_t>(readLine(builderOut.readSide.get()), tmp)) abort(); pid = tmp; - /* Set the UID/GID mapping of the builder's user namespace - such that the sandbox user maps to the build user, or to - the calling user (if build users are disabled). */ - uid_t hostUid = buildUser.enabled() ? buildUser.getUID() : getuid(); - uid_t hostGid = buildUser.enabled() ? buildUser.getGID() : getgid(); + /* Set the UID/GID mapping of the builder's user + namespace such that root maps to the build user, or to the + calling user (if build users are disabled). */ + uid_t targetUid = buildUser.enabled() ? buildUser.getUID() : getuid(); + uid_t targetGid = buildUser.enabled() ? buildUser.getGID() : getgid(); writeFile("/proc/" + std::to_string(pid) + "/uid_map", - (format("%d %d 1") % sandboxUid % hostUid).str()); + (format("0 %d 1") % targetUid).str()); writeFile("/proc/" + std::to_string(pid) + "/setgroups", "deny"); writeFile("/proc/" + std::to_string(pid) + "/gid_map", - (format("%d %d 1") % sandboxGid % hostGid).str()); + (format("0 %d 1") % targetGid).str()); /* Signal the builder that we've updated its user namespace. */ @@ -2420,12 +2457,11 @@ void DerivationGoal::runChild() if (rmdir("real-root") == -1) throw SysError("cannot remove real-root directory"); - /* Switch to the sandbox uid/gid in the user namespace, - which corresponds to the build user or calling user in - the parent namespace. */ - if (setgid(sandboxGid) == -1) + /* Become root in the user namespace, which corresponds to + the build user or calling user in the parent namespace. */ + if (setgid(0) == -1) throw SysError("setgid failed"); - if (setuid(sandboxUid) == -1) + if (setuid(0) == -1) throw SysError("setuid failed"); setUser = false; diff --git a/src/libstore/local.mk b/src/libstore/local.mk index 9d5c04dca..a8222025c 100644 --- a/src/libstore/local.mk +++ b/src/libstore/local.mk @@ -18,6 +18,10 @@ ifeq ($(OS), SunOS) libstore_LDFLAGS += -lsocket endif +ifeq ($(OS), Linux) + libstore_LDFLAGS += -lseccomp +endif + libstore_CXXFLAGS = \ -DNIX_PREFIX=\"$(prefix)\" \ -DNIX_STORE_DIR=\"$(storedir)\" \ diff --git a/tests/sandbox.nix b/tests/sandbox.nix new file mode 100644 index 000000000..dc72a5985 --- /dev/null +++ b/tests/sandbox.nix @@ -0,0 +1,54 @@ +# Test Nix builder sandbox. + +{ system, nix }: + +with import <nixpkgs/nixos/lib/testing.nix> { inherit system; }; + +let + mkUtils = pkgs: pkgs.buildEnv { + name = "sandbox-utils"; + paths = [ pkgs.coreutils pkgs.utillinux pkgs.bash ]; + pathsToLink = [ "/bin" "/sbin" ]; + }; + + utils32 = mkUtils pkgs.pkgsi686Linux; + utils64 = mkUtils pkgs; + + sandboxTestScript = pkgs.writeText "sandbox-testscript.sh" '' + [ $(id -u) -eq 0 ] + cp -p "$testfile" foo + chown 1024:1024 foo + touch "$out" + ''; + + testExpr = arch: pkgs.writeText "sandbox-test.nix" '' + let + utils = builtins.storePath + ${if arch == "i686-linux" then utils32 else utils64}; + in derivation { + name = "sandbox-test"; + system = "${arch}"; + builder = "''${utils}/bin/bash"; + args = ["-e" ${sandboxTestScript}]; + PATH = "''${utils}/bin"; + testfile = builtins.toFile "test" "i am a test file"; + } + ''; + +in makeTest { + name = "nix-sandbox"; + + machine = { pkgs, ... }: { + nix.package = nix; + nix.useSandbox = true; + nix.binaryCaches = []; + virtualisation.writableStore = true; + virtualisation.pathsInNixDB = [ utils32 utils64 ]; + }; + + testScript = '' + $machine->waitForUnit("multi-user.target"); + $machine->succeed("nix-build ${testExpr "x86_64-linux"}"); + $machine->succeed("nix-build ${testExpr "i686-linux"}"); + ''; +} |