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authorjln@chromium.org <jln@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98>2013-11-26 03:32:28 +0000
committerjln@chromium.org <jln@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98>2013-11-26 03:32:28 +0000
commit389cad51b0123c31a453f9fee8abd23a5e5c3b80 (patch)
treed3001311f01c7d6c10793b17f64dccf2d962913c /sandbox
parent37dacfae5e70134813abc97e59e6f4d44e70fff1 (diff)
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Linux sandbox: move CurrentProcessHasOpenDirectories
Move CurrentProcessHasOpenDirectories() to the Credentials class and rename it to HasOpenDirectory(). Also add some unittests. BUG=312380 R=jorgelo@chromium.org Review URL: https://codereview.chromium.org/85403011 git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237242 0039d316-1c4b-4281-b951-d872f2087c98
Diffstat (limited to 'sandbox')
-rw-r--r--sandbox/linux/services/credentials.cc61
-rw-r--r--sandbox/linux/services/credentials.h19
-rw-r--r--sandbox/linux/services/credentials_unittest.cc44
3 files changed, 121 insertions, 3 deletions
diff --git a/sandbox/linux/services/credentials.cc b/sandbox/linux/services/credentials.cc
index 0af5a42b..cea757c 100644
--- a/sandbox/linux/services/credentials.cc
+++ b/sandbox/linux/services/credentials.cc
@@ -4,9 +4,13 @@
#include "sandbox/linux/services/credentials.h"
+#include <dirent.h>
#include <errno.h>
+#include <fcntl.h>
#include <stdio.h>
#include <sys/capability.h>
+#include <sys/stat.h>
+#include <sys/types.h>
#include <unistd.h>
#include "base/basictypes.h"
@@ -49,6 +53,15 @@ struct FILECloser {
// 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;
@@ -143,6 +156,51 @@ Credentials::Credentials() {
Credentials::~Credentials() {
}
+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 not available, guess false.
+ // TODO(mostynb@opera.com): add a CHECK_EQ(ENOENT, errno); Figure out what
+ // other situations are here. http://crbug.com/314985
+ return false;
+ }
+ }
+ CHECK_GE(proc_self_fd, 0);
+
+ // 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);
@@ -199,6 +257,9 @@ bool Credentials::MoveToNewUserNS() {
}
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();
}
diff --git a/sandbox/linux/services/credentials.h b/sandbox/linux/services/credentials.h
index 80b2ec1..c23db93 100644
--- a/sandbox/linux/services/credentials.h
+++ b/sandbox/linux/services/credentials.h
@@ -26,6 +26,20 @@ class Credentials {
Credentials();
~Credentials();
+ // Checks whether the current process has any directory file descriptor open.
+ // Directory file descriptors are "capabilities" that would let a process use
+ // system calls such as openat() to bypass restrictions such as
+ // DropFileSystemAccess().
+ // Sometimes it's useful to call HasOpenDirectory() after file system access
+ // has been dropped. In this case, |proc_fd| should be a file descriptor to
+ // /proc. The file descriptor in |proc_fd| will be ignored by
+ // HasOpenDirectory() and remains owned by the caller. It is very important
+ // for the caller to close it.
+ // If /proc is available, |proc_fd| can be passed as -1.
+ // If |proc_fd| is -1 and /proc is not available, this function will return
+ // false.
+ bool HasOpenDirectory(int proc_fd);
+
// Drop all capabilities in the effective, inheritable and permitted sets for
// the current process.
bool DropAllCapabilities();
@@ -52,9 +66,8 @@ class Credentials {
// CAP_SYS_CHROOT can be acquired by using the MoveToNewUserNS() API.
// Make sure to call DropAllCapabilities() after this call to prevent
// escapes.
- // To be secure, it's very important for this API to not be called with any
- // directory file descriptor present. TODO(jln): integrate with
- // crbug.com/269806 when available.
+ // To be secure, it's very important for this API to not be called while the
+ // process has any directory file descriptor open.
bool DropFileSystemAccess();
private:
diff --git a/sandbox/linux/services/credentials_unittest.cc b/sandbox/linux/services/credentials_unittest.cc
index da61cd5..9160bf7 100644
--- a/sandbox/linux/services/credentials_unittest.cc
+++ b/sandbox/linux/services/credentials_unittest.cc
@@ -5,14 +5,20 @@
#include "sandbox/linux/services/credentials.h"
#include <errno.h>
+#include <fcntl.h>
#include <stdio.h>
+#include <sys/stat.h>
+#include <sys/types.h>
#include <unistd.h>
+#include "base/file_util.h"
#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "sandbox/linux/tests/unit_tests.h"
#include "testing/gtest/include/gtest/gtest.h"
+using file_util::ScopedFD;
+
namespace sandbox {
namespace {
@@ -52,6 +58,44 @@ TEST(Credentials, CreateAndDestroy) {
scoped_ptr<Credentials> cred2(new Credentials);
}
+TEST(Credentials, HasOpenDirectory) {
+ Credentials creds;
+ // No open directory should exist at startup.
+ EXPECT_FALSE(creds.HasOpenDirectory(-1));
+ {
+ // Have a "/dev" file descriptor around.
+ int dev_fd = open("/dev", O_RDONLY | O_DIRECTORY);
+ ScopedFD dev_fd_closer(&dev_fd);
+ EXPECT_TRUE(creds.HasOpenDirectory(-1));
+ }
+ EXPECT_FALSE(creds.HasOpenDirectory(-1));
+}
+
+TEST(Credentials, HasOpenDirectoryWithFD) {
+ Credentials creds;
+
+ int proc_fd = open("/proc", O_RDONLY | O_DIRECTORY);
+ ScopedFD proc_fd_closer(&proc_fd);
+ ASSERT_LE(0, proc_fd);
+
+ // Don't pass |proc_fd|, an open directory (proc_fd) should
+ // be detected.
+ EXPECT_TRUE(creds.HasOpenDirectory(-1));
+ // Pass |proc_fd| and no open directory should be detected.
+ EXPECT_FALSE(creds.HasOpenDirectory(proc_fd));
+
+ {
+ // Have a "/dev" file descriptor around.
+ int dev_fd = open("/dev", O_RDONLY | O_DIRECTORY);
+ ScopedFD dev_fd_closer(&dev_fd);
+ EXPECT_TRUE(creds.HasOpenDirectory(proc_fd));
+ }
+
+ // The "/dev" file descriptor should now be closed, |proc_fd| is the only
+ // directory file descriptor open.
+ EXPECT_FALSE(creds.HasOpenDirectory(proc_fd));
+}
+
SANDBOX_TEST(Credentials, DropAllCaps) {
Credentials creds;
CHECK(creds.DropAllCapabilities());