diff options
Diffstat (limited to 'src/libstore')
| -rw-r--r-- | src/libstore/build.cc | 94 | ||||
| -rw-r--r-- | src/libstore/local.mk | 4 |
2 files changed, 69 insertions, 29 deletions
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)\" \ |