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Unified Diff: sandbox/linux/services/credentials.cc

Issue 670183003: Update from chromium 62675d9fb31fb8cedc40f68e78e8445a74f362e7 (Closed) Base URL: git@github.com:domokit/mojo.git@master
Patch Set: Created 6 years, 2 months ago
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Index: sandbox/linux/services/credentials.cc
diff --git a/sandbox/linux/services/credentials.cc b/sandbox/linux/services/credentials.cc
new file mode 100644
index 0000000000000000000000000000000000000000..96702b1700a9cc9626696b5eaadaa7e5f83e219e
--- /dev/null
+++ b/sandbox/linux/services/credentials.cc
@@ -0,0 +1,347 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sandbox/linux/services/credentials.h"
+
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdio.h>
+#include <sys/capability.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "base/basictypes.h"
+#include "base/bind.h"
+#include "base/logging.h"
+#include "base/posix/eintr_wrapper.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/template_util.h"
+#include "base/third_party/valgrind/valgrind.h"
+#include "base/threading/thread.h"
+
+namespace {
+
+bool IsRunningOnValgrind() { return RUNNING_ON_VALGRIND; }
+
+struct CapFreeDeleter {
+ inline void operator()(cap_t cap) const {
+ int ret = cap_free(cap);
+ CHECK_EQ(0, ret);
+ }
+};
+
+// Wrapper to manage libcap2's cap_t type.
+typedef scoped_ptr<typeof(*((cap_t)0)), CapFreeDeleter> ScopedCap;
+
+struct CapTextFreeDeleter {
+ inline void operator()(char* cap_text) const {
+ int ret = cap_free(cap_text);
+ CHECK_EQ(0, ret);
+ }
+};
+
+// Wrapper to manage the result from libcap2's cap_from_text().
+typedef scoped_ptr<char, CapTextFreeDeleter> ScopedCapText;
+
+struct FILECloser {
+ inline void operator()(FILE* f) const {
+ DCHECK(f);
+ PCHECK(0 == fclose(f));
+ }
+};
+
+// Don't use ScopedFILE in base since it doesn't check fclose().
+// TODO(jln): fix base/.
+typedef scoped_ptr<FILE, FILECloser> ScopedFILE;
+
+struct DIRCloser {
+ void operator()(DIR* d) const {
+ DCHECK(d);
+ PCHECK(0 == closedir(d));
+ }
+};
+
+typedef scoped_ptr<DIR, DIRCloser> ScopedDIR;
+
+COMPILE_ASSERT((base::is_same<uid_t, gid_t>::value), UidAndGidAreSameType);
+// generic_id_t can be used for either uid_t or gid_t.
+typedef uid_t generic_id_t;
+
+// Write a uid or gid mapping from |id| to |id| in |map_file|.
+bool WriteToIdMapFile(const char* map_file, generic_id_t id) {
+ ScopedFILE f(fopen(map_file, "w"));
+ PCHECK(f);
+ const uid_t inside_id = id;
+ const uid_t outside_id = id;
+ int num = fprintf(f.get(), "%d %d 1\n", inside_id, outside_id);
+ if (num < 0) return false;
+ // Manually call fflush() to catch permission failures.
+ int ret = fflush(f.get());
+ if (ret) {
+ VLOG(1) << "Could not write to id map file";
+ return false;
+ }
+ return true;
+}
+
+// Checks that the set of RES-uids and the set of RES-gids have
+// one element each and return that element in |resuid| and |resgid|
+// respectively. It's ok to pass NULL as one or both of the ids.
+bool GetRESIds(uid_t* resuid, gid_t* resgid) {
+ uid_t ruid, euid, suid;
+ gid_t rgid, egid, sgid;
+ PCHECK(getresuid(&ruid, &euid, &suid) == 0);
+ PCHECK(getresgid(&rgid, &egid, &sgid) == 0);
+ const bool uids_are_equal = (ruid == euid) && (ruid == suid);
+ const bool gids_are_equal = (rgid == egid) && (rgid == sgid);
+ if (!uids_are_equal || !gids_are_equal) return false;
+ if (resuid) *resuid = euid;
+ if (resgid) *resgid = egid;
+ return true;
+}
+
+// chroot() and chdir() to /proc/<tid>/fdinfo.
+void ChrootToThreadFdInfo(base::PlatformThreadId tid, bool* result) {
+ DCHECK(result);
+ *result = false;
+
+ COMPILE_ASSERT((base::is_same<base::PlatformThreadId, int>::value),
+ TidIsAnInt);
+ const std::string current_thread_fdinfo = "/proc/" +
+ base::IntToString(tid) + "/fdinfo/";
+
+ // Make extra sure that /proc/<tid>/fdinfo is unique to the thread.
+ CHECK(0 == unshare(CLONE_FILES));
+ int chroot_ret = chroot(current_thread_fdinfo.c_str());
+ if (chroot_ret) {
+ PLOG(ERROR) << "Could not chroot";
+ return;
+ }
+
+ // CWD is essentially an implicit file descriptor, so be careful to not leave
+ // it behind.
+ PCHECK(0 == chdir("/"));
+
+ *result = true;
+ return;
+}
+
+// chroot() to an empty dir that is "safe". To be safe, it must not contain
+// any subdirectory (chroot-ing there would allow a chroot escape) and it must
+// be impossible to create an empty directory there.
+// We achieve this by doing the following:
+// 1. We create a new thread, which will create a new /proc/<tid>/ directory
+// 2. We chroot to /proc/<tid>/fdinfo/
+// This is already "safe", since fdinfo/ does not contain another directory and
+// one cannot create another directory there.
+// 3. The thread dies
+// After (3) happens, the directory is not available anymore in /proc.
+bool ChrootToSafeEmptyDir() {
+ base::Thread chrooter("sandbox_chrooter");
+ if (!chrooter.Start()) return false;
+ bool is_chrooted = false;
+ chrooter.message_loop()->PostTask(FROM_HERE,
+ base::Bind(&ChrootToThreadFdInfo, chrooter.thread_id(), &is_chrooted));
+ // Make sure our task has run before committing the return value.
+ chrooter.Stop();
+ return is_chrooted;
+}
+
+// CHECK() that an attempt to move to a new user namespace raised an expected
+// errno.
+void CheckCloneNewUserErrno(int error) {
+ // EPERM can happen if already in a chroot. EUSERS if too many nested
+ // namespaces are used. EINVAL for kernels that don't support the feature.
+ // Valgrind will ENOSYS unshare().
+ PCHECK(error == EPERM || error == EUSERS || error == EINVAL ||
+ error == ENOSYS);
+}
+
+} // namespace.
+
+namespace sandbox {
+
+Credentials::Credentials() {
+}
+
+Credentials::~Credentials() {
+}
+
+int Credentials::CountOpenFds(int proc_fd) {
+ DCHECK_LE(0, proc_fd);
+ int proc_self_fd = openat(proc_fd, "self/fd", O_DIRECTORY | O_RDONLY);
+ PCHECK(0 <= proc_self_fd);
+
+ // Ownership of proc_self_fd is transferred here, it must not be closed
+ // or modified afterwards except via dir.
+ ScopedDIR dir(fdopendir(proc_self_fd));
+ CHECK(dir);
+
+ int count = 0;
+ struct dirent e;
+ struct dirent* de;
+ while (!readdir_r(dir.get(), &e, &de) && de) {
+ if (strcmp(e.d_name, ".") == 0 || strcmp(e.d_name, "..") == 0) {
+ continue;
+ }
+
+ int fd_num;
+ CHECK(base::StringToInt(e.d_name, &fd_num));
+ if (fd_num == proc_fd || fd_num == proc_self_fd) {
+ continue;
+ }
+
+ ++count;
+ }
+ return count;
+}
+
+bool Credentials::HasOpenDirectory(int proc_fd) {
+ int proc_self_fd = -1;
+ if (proc_fd >= 0) {
+ proc_self_fd = openat(proc_fd, "self/fd", O_DIRECTORY | O_RDONLY);
+ } else {
+ proc_self_fd = openat(AT_FDCWD, "/proc/self/fd", O_DIRECTORY | O_RDONLY);
+ if (proc_self_fd < 0) {
+ // If this process has been chrooted (eg into /proc/self/fdinfo) then
+ // the new root dir will not have directory listing permissions for us
+ // (hence EACCES). And if we do have this permission, then /proc won't
+ // exist anyway (hence ENOENT).
+ DPCHECK(errno == EACCES || errno == ENOENT)
+ << "Unexpected failure when trying to open /proc/self/fd: ("
+ << errno << ") " << strerror(errno);
+
+ // If not available, guess false.
+ return false;
+ }
+ }
+ PCHECK(0 <= proc_self_fd);
+
+ // Ownership of proc_self_fd is transferred here, it must not be closed
+ // or modified afterwards except via dir.
+ ScopedDIR dir(fdopendir(proc_self_fd));
+ CHECK(dir);
+
+ struct dirent e;
+ struct dirent* de;
+ while (!readdir_r(dir.get(), &e, &de) && de) {
+ if (strcmp(e.d_name, ".") == 0 || strcmp(e.d_name, "..") == 0) {
+ continue;
+ }
+
+ int fd_num;
+ CHECK(base::StringToInt(e.d_name, &fd_num));
+ if (fd_num == proc_fd || fd_num == proc_self_fd) {
+ continue;
+ }
+
+ struct stat s;
+ // It's OK to use proc_self_fd here, fstatat won't modify it.
+ CHECK(fstatat(proc_self_fd, e.d_name, &s, 0) == 0);
+ if (S_ISDIR(s.st_mode)) {
+ return true;
+ }
+ }
+
+ // No open unmanaged directories found.
+ return false;
+}
+
+bool Credentials::DropAllCapabilities() {
+ ScopedCap cap(cap_init());
+ CHECK(cap);
+ PCHECK(0 == cap_set_proc(cap.get()));
+ // We never let this function fail.
+ return true;
+}
+
+bool Credentials::HasAnyCapability() const {
+ ScopedCap current_cap(cap_get_proc());
+ CHECK(current_cap);
+ ScopedCap empty_cap(cap_init());
+ CHECK(empty_cap);
+ return cap_compare(current_cap.get(), empty_cap.get()) != 0;
+}
+
+scoped_ptr<std::string> Credentials::GetCurrentCapString() const {
+ ScopedCap current_cap(cap_get_proc());
+ CHECK(current_cap);
+ ScopedCapText cap_text(cap_to_text(current_cap.get(), NULL));
+ CHECK(cap_text);
+ return scoped_ptr<std::string> (new std::string(cap_text.get()));
+}
+
+// static
+bool Credentials::SupportsNewUserNS() {
+ // Valgrind will let clone(2) pass-through, but doesn't support unshare(),
+ // so always consider UserNS unsupported there.
+ if (IsRunningOnValgrind()) {
+ return false;
+ }
+
+ // This is roughly a fork().
+ const pid_t pid = syscall(__NR_clone, CLONE_NEWUSER | SIGCHLD, 0, 0, 0);
+
+ if (pid == -1) {
+ CheckCloneNewUserErrno(errno);
+ return false;
+ }
+
+ // The parent process could have had threads. In the child, these threads
+ // have disappeared. Make sure to not do anything in the child, as this is a
+ // fragile execution environment.
+ if (pid == 0) {
+ _exit(0);
+ }
+
+ // Always reap the child.
+ siginfo_t infop;
+ PCHECK(0 == HANDLE_EINTR(waitid(P_PID, pid, &infop, WEXITED)));
+
+ // clone(2) succeeded, we can use CLONE_NEWUSER.
+ return true;
+}
+
+bool Credentials::MoveToNewUserNS() {
+ uid_t uid;
+ gid_t gid;
+ if (!GetRESIds(&uid, &gid)) {
+ // If all the uids (or gids) are not equal to each other, the security
+ // model will most likely confuse the caller, abort.
+ DVLOG(1) << "uids or gids differ!";
+ return false;
+ }
+ int ret = unshare(CLONE_NEWUSER);
+ if (ret) {
+ const int unshare_errno = errno;
+ VLOG(1) << "Looks like unprivileged CLONE_NEWUSER may not be available "
+ << "on this kernel.";
+ CheckCloneNewUserErrno(unshare_errno);
+ return false;
+ }
+
+ // The current {r,e,s}{u,g}id is now an overflow id (c.f.
+ // /proc/sys/kernel/overflowuid). Setup the uid and gid maps.
+ DCHECK(GetRESIds(NULL, NULL));
+ const char kGidMapFile[] = "/proc/self/gid_map";
+ const char kUidMapFile[] = "/proc/self/uid_map";
+ CHECK(WriteToIdMapFile(kGidMapFile, gid));
+ CHECK(WriteToIdMapFile(kUidMapFile, uid));
+ DCHECK(GetRESIds(NULL, NULL));
+ return true;
+}
+
+bool Credentials::DropFileSystemAccess() {
+ // Chrooting to a safe empty dir will only be safe if no directory file
+ // descriptor is available to the process.
+ DCHECK(!HasOpenDirectory(-1));
+ return ChrootToSafeEmptyDir();
+}
+
+} // namespace sandbox.
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