diff options
| -rw-r--r-- | src/libstore/build.cc | 47 |
1 files changed, 31 insertions, 16 deletions
diff --git a/src/libstore/build.cc b/src/libstore/build.cc index b812d1668bc5..7b881941e111 100644 --- a/src/libstore/build.cc +++ b/src/libstore/build.cc @@ -804,6 +804,9 @@ 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); @@ -1941,14 +1944,18 @@ void DerivationGoal::startBuilder() createDirs(chrootRootDir + "/etc"); writeFile(chrootRootDir + "/etc/passwd", - "root:x:0:0:Nix build user:/:/noshell\n" - "nobody:x:65534:65534:Nobody:/:/noshell\n"); + (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()); /* Declare the build user's group so that programs get a consistent view of the system (e.g., "id -gn"). */ writeFile(chrootRootDir + "/etc/group", - "root:x:0:\n" - "nobody:x:65534:\n"); + (format( + "root:x:0:\n" + "nixbld:!:%1%:\n" + "nogroup:x:65534:\n") % sandboxGid).str()); /* Create /etc/hosts with localhost entry. */ if (!fixedOutput) @@ -2130,7 +2137,12 @@ void DerivationGoal::startBuilder() Pid helper = startProcess([&]() { /* Drop additional groups here because we can't do it - after we've created the new user namespace. */ + 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)?)*/ if (getuid() == 0 && setgroups(0, 0) == -1) throw SysError("setgroups failed"); @@ -2163,19 +2175,19 @@ 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 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(); + /* 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(); writeFile("/proc/" + std::to_string(pid) + "/uid_map", - (format("0 %d 1") % targetUid).str()); + (format("%d %d 1") % sandboxUid % hostUid).str()); writeFile("/proc/" + std::to_string(pid) + "/setgroups", "deny"); writeFile("/proc/" + std::to_string(pid) + "/gid_map", - (format("0 %d 1") % targetGid).str()); + (format("%d %d 1") % sandboxGid % hostGid).str()); /* Signal the builder that we've updated its user namespace. */ @@ -2341,6 +2353,7 @@ void DerivationGoal::runChild() requires the kernel to be compiled with CONFIG_DEVPTS_MULTIPLE_INSTANCES=y (which is the case if /dev/ptx/ptmx exists). */ +#if 0 if (pathExists("/dev/pts/ptmx") && !pathExists(chrootRootDir + "/dev/ptmx") && dirsInChroot.find("/dev/pts") == dirsInChroot.end()) @@ -2353,6 +2366,7 @@ void DerivationGoal::runChild() Linux versions, it is created with permissions 0. */ chmod_(chrootRootDir + "/dev/pts/ptmx", 0666); } +#endif /* Do the chroot(). */ if (chdir(chrootRootDir.c_str()) == -1) @@ -2373,11 +2387,12 @@ void DerivationGoal::runChild() if (rmdir("real-root") == -1) throw SysError("cannot remove real-root directory"); - /* Become root in the user namespace, which corresponds to - the build user or calling user in the parent namespace. */ - if (setgid(0) == -1) + /* 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) throw SysError("setgid failed"); - if (setuid(0) == -1) + if (setuid(sandboxUid) == -1) throw SysError("setuid failed"); setUser = false; |