Linux: add basic unprivileged namespace support.

sandbox/linux/services/credentials_unittest.cc

Index: sandbox/linux/services/credentials_unittest.cc
diff --git a/sandbox/linux/services/credentials_unittest.cc b/sandbox/linux/services/credentials_unittest.cc
index 7c705a41043d294bbeb1e6b670b14798585d3b9a..355d4ab5e4a61043750247f103e9c3d46ecd1f93 100644
--- a/sandbox/linux/services/credentials_unittest.cc
+++ b/sandbox/linux/services/credentials_unittest.cc
@@ -4,6 +4,9 @@
 
 #include "sandbox/linux/services/credentials.h"
 
+#include <errno.h>
+#include <unistd.h>
+
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "sandbox/linux/tests/unit_tests.h"
@@ -11,6 +14,34 @@
 
 namespace sandbox {
 
+namespace {
+
+bool DirectoryExists(const char* path) {
+  struct stat dir;
+  errno = 0;
+  int ret = stat(path, &dir);
+  return -1 != ret || ENOENT != errno;
+}
+
+bool WorkingDirectoryIsRoot() {
+  char current_dir[PATH_MAX];
+  char* cwd = getcwd(current_dir, sizeof(current_dir));
+  PCHECK(cwd);
+  if (strcmp("/", cwd)) return false;
+
+  // The current directory is the root. Add a few paranoid checks.
+  struct stat current;
+  CHECK_EQ(0, stat(".", &current));
+  struct stat parrent;
+  CHECK_EQ(0, stat("..", &parrent));
+  CHECK_EQ(current.st_dev, parrent.st_dev);
+  CHECK_EQ(current.st_ino, parrent.st_ino);
+  CHECK_EQ(current.st_mode, parrent.st_mode);
+  CHECK_EQ(current.st_uid, parrent.st_uid);
+  CHECK_EQ(current.st_gid, parrent.st_gid);
+  return true;
+}
+
 // Give dynamic tools a simple thing to test.
 TEST(Credentials, CreateAndDestroy) {
   {
@@ -22,15 +53,116 @@ TEST(Credentials, CreateAndDestroy) {
 
 SANDBOX_TEST(Credentials, DropAllCaps) {
   Credentials creds;
-  creds.DropAllCapabilities();
-  SANDBOX_ASSERT(!creds.HasAnyCapability());
+  CHECK(creds.DropAllCapabilities());
+  CHECK(!creds.HasAnyCapability());
 }
 
 SANDBOX_TEST(Credentials, GetCurrentCapString) {
   Credentials creds;
-  creds.DropAllCapabilities();
+  CHECK(creds.DropAllCapabilities());
   const char kNoCapabilityText[] = "=";
-  SANDBOX_ASSERT(*creds.GetCurrentCapString() == kNoCapabilityText);
+  CHECK(*creds.GetCurrentCapString() == kNoCapabilityText);
+}
+
+SANDBOX_TEST(Credentials, MoveToNewUserNS) {
+  Credentials creds;
+  creds.DropAllCapabilities();
+  bool userns_supported = creds.MoveToNewUserNS();
+  printf("Unprivileged CLONE_NEWUSER supported: %s\n",
+         userns_supported ? "true." : "false.");
+  if (!userns_supported) {
+    printf("This kernel does not support unprivileged namespaces. "
+           "USERNS tests will all pass.\n");
+    return;
+  }
+  CHECK(creds.HasAnyCapability());
+  creds.DropAllCapabilities();
+  CHECK(!creds.HasAnyCapability());
+}
+
+SANDBOX_TEST(Credentials, UidIsPreserved) {
+  Credentials creds;
+  creds.DropAllCapabilities();
+  uid_t old_ruid, old_euid, old_suid;
+  gid_t old_rgid, old_egid, old_sgid;
+  PCHECK(0 == getresuid(&old_ruid, &old_euid, &old_suid));
+  PCHECK(0 == getresgid(&old_rgid, &old_egid, &old_sgid));
+  // Probably missing kernel support.
+  if (!creds.MoveToNewUserNS()) return;
+  uid_t new_ruid, new_euid, new_suid;
+  PCHECK(0 == getresuid(&new_ruid, &new_euid, &new_suid));
+  CHECK(old_ruid == new_ruid);
+  CHECK(old_euid == new_euid);
+  CHECK(old_suid == new_suid);
+
+  gid_t new_rgid, new_egid, new_sgid;
+  PCHECK(0 == getresgid(&new_rgid, &new_egid, &new_sgid));
+  CHECK(old_rgid == new_rgid);
+  CHECK(old_egid == new_egid);
+  CHECK(old_sgid == new_sgid);
+}
+
+bool NewUserNSCycle(Credentials* creds) {
+  DCHECK(creds);
+  if (!creds->MoveToNewUserNS() ||
+      !creds->HasAnyCapability() ||
+      !creds->DropAllCapabilities() ||
+      creds->HasAnyCapability()) {
+    return false;
+  }
+  return true;
+}
+
+SANDBOX_TEST(Credentials, NestedUserNS) {
+  Credentials creds;
+  CHECK(creds.DropAllCapabilities());
+  // Probably missing kernel support.
+  if (!creds.MoveToNewUserNS()) return;
+  creds.DropAllCapabilities();
+  // As of 3.12, the kernel has a limit of 32. See create_user_ns().
+  const int kNestLevel = 10;
+  for (int i = 0; i < kNestLevel; ++i) {
+    CHECK(NewUserNSCycle(&creds)) << "Creating new user NS failed at iteration "
+                                  << i << ".";
+  }
 }
 
+// Test the WorkingDirectoryIsRoot() helper.
+TEST(Credentials, CanDetectRoot) {
+  ASSERT_EQ(0, chdir("/proc/"));
+  ASSERT_FALSE(WorkingDirectoryIsRoot());
+  ASSERT_EQ(0, chdir("/"));
+  ASSERT_TRUE(WorkingDirectoryIsRoot());
+}
+
+SANDBOX_TEST(Credentials, DropFileSystemAccessIsSafe) {
+  Credentials creds;
+  CHECK(creds.DropAllCapabilities());
+  // Probably missing kernel support.
+  if (!creds.MoveToNewUserNS()) return;
+  CHECK(creds.DropFileSystemAccess());
+  CHECK(!DirectoryExists("/proc"));
+  CHECK(WorkingDirectoryIsRoot());
+  // We want the chroot to never have a subdirectory. A subdirectory
+  // could allow a chroot escape.
+  CHECK_NE(0, mkdir("/test", 0700));
+}
+
+// Check that after dropping filesystem access and dropping privileges
+// it is not possible to regain capabilities.
+SANDBOX_TEST(Credentials, CannotRegainPrivileges) {
+  Credentials creds;
+  CHECK(creds.DropAllCapabilities());
+  // Probably missing kernel support.
+  if (!creds.MoveToNewUserNS()) return;
+  CHECK(creds.DropFileSystemAccess());
+  CHECK(creds.DropAllCapabilities());
+
+  // The kernel should now prevent us from regaining capabilities because we
+  // are in a chroot.
+  CHECK(!creds.MoveToNewUserNS());
+}
+
+}  // namespace.
+
 }  // namespace sandbox.