Sandbox: Add support for file system policies that use implied device paths.

sandbox/win/src/win_utils.cc

Index: sandbox/win/src/win_utils.cc
diff --git a/sandbox/win/src/win_utils.cc b/sandbox/win/src/win_utils.cc
index 12f818926b4bdb642efc658644b6b9e75ca19e22..6b0f747e3a06e9d7f90f5bc4fd9b5c89d25b49c3 100644
--- a/sandbox/win/src/win_utils.cc
+++ b/sandbox/win/src/win_utils.cc
@@ -9,6 +9,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string_util.h"
 #include "base/win/pe_image.h"
+#include "base/win/windows_version.h"
 #include "sandbox/win/src/internal_types.h"
 #include "sandbox/win/src/nt_internals.h"
 #include "sandbox/win/src/sandbox_nt_util.h"
@@ -34,19 +35,68 @@ const KnownReservedKey kKnownKey[] = {
     { L"HKEY_DYN_DATA", HKEY_DYN_DATA}
 };
 
+// Returns true if |path| starts with "\??\" and returns a path without that
+// component.
+bool IsNTPath(const base::string16& path, base::string16* trimmed_path ) {
+  if ((path.size() < sandbox::kNTPrefixLen) ||
+      (0 != path.compare(0, sandbox::kNTPrefixLen, sandbox::kNTPrefix))) {
+    *trimmed_path = path;
+    return false;
+  }
+
+  *trimmed_path = path.substr(sandbox::kNTPrefixLen);
+  return true;
+}
+
+// Returns true if |path| starts with "\Device\" and returns a path without that
+// component.
+bool IsDevicePath(const base::string16& path, base::string16* trimmed_path ) {

[cpu_(ooo_6.6-7.5), 2015/02/13 19:27:37]

name: TrimDevicePath() ?

and above TrimNtPath() ?

[rvargas (doing something else), 2015/02/13 19:43:05]

Not so sure. I want the "main" function to be the implied by the return value
("is this a foo kind of path?"). The first version had the out argument as
optional but all users were passing a value so I removed that feature.

I don't think it is worth splitting this in two functions: check + trim.

See line 227

[cpu_(ooo_6.6-7.5), 2015/02/17 21:59:45]

Acknowledged.

+  if ((path.size() < sandbox::kNTDevicePrefixLen) ||
+      (0 != _wcsnicmp(path.c_str(), sandbox::kNTDevicePrefix,
+                      sandbox::kNTDevicePrefixLen))) {
+    *trimmed_path = path;
+    return false;
+  }
+
+  *trimmed_path = path.substr(sandbox::kNTDevicePrefixLen);
+  return true;
+}
+
+bool StartsWithDriveLetter(const base::string16& path) {
+  if (path.size() < 3)
+    return false;
+
+  if (path[1] != L':' || path[2] != L'\\')
+    return false;
+

[cpu_(ooo_6.6-7.5), 2015/02/13 19:27:37]

I think the thing below is
http://en.cppreference.com/w/cpp/string/byte/isalpha

[rvargas (doing something else), 2015/02/13 19:43:05]

That is locale dependent and a drive letter is not.

[cpu_(ooo_6.6-7.5), 2015/02/17 21:59:45]

Acknowledged.

+  return (path[0] >= 'a' && path[0] <= 'z') ||
+         (path[0] >= 'A' && path[0] <= 'Z');
+}
+
+const wchar_t kNTDotPrefix[] = L"\\\\.\\";
+const size_t kNTDotPrefixLen = arraysize(kNTDotPrefix) - 1;
+
+// Removes "\\\\.\\" from the path.
+void RemoveImpliedDevice(base::string16* path) {
+  if (0 == path->compare(0, kNTDotPrefixLen, kNTDotPrefix))
+    *path = path->substr(kNTDotPrefixLen);
+}
+
 }  // namespace
 
 namespace sandbox {
 
 // Returns true if the provided path points to a pipe.
 bool IsPipe(const base::string16& path) {
-  base::string16 lower_path = base::StringToLowerASCII(path);

[cpu_(ooo_6.6-7.5), 2015/02/13 19:27:37]

without this helper do we still need to include string_util ?

   size_t start = 0;
-  if (0 == lower_path.compare(0, sandbox::kNTPrefixLen, sandbox::kNTPrefix))
+  if (0 == path.compare(0, sandbox::kNTPrefixLen, sandbox::kNTPrefix))
     start = sandbox::kNTPrefixLen;
 
   const wchar_t kPipe[] = L"pipe\\";
-  return (0 == lower_path.compare(start, arraysize(kPipe) - 1, kPipe));
+  if (path.size() < start + arraysize(kPipe) - 1)
+    return false;
+
+  return (0 == _wcsnicmp(path.c_str() + start, kPipe, arraysize(kPipe) - 1));
 }
 
 HKEY GetReservedKeyFromName(const base::string16& name) {
@@ -82,20 +132,38 @@ bool ResolveRegistryName(base::string16 name, base::string16* resolved_name) {
   return false;
 }
 
+// |full_path| can have any of the following forms:
+//    \??\c:\some\foo\bar
+//    \Device\HarddiskVolume0\some\foo\bar
+//    \??\HarddiskVolume0\some\foo\bar
+// For OSes before Win7, anything but the first form will be rejected.
 DWORD IsReparsePoint(const base::string16& full_path, bool* result) {
-  base::string16 path = full_path;
-
-  // Remove the nt prefix.
-  if (0 == path.compare(0, kNTPrefixLen, kNTPrefix))
-    path = path.substr(kNTPrefixLen);
-
   // Check if it's a pipe. We can't query the attributes of a pipe.
-  if (IsPipe(path)) {
+  if (IsPipe(full_path)) {
     *result = FALSE;
     return ERROR_SUCCESS;
   }
 
+  base::string16 path;
+  bool nt_path = IsNTPath(full_path, &path);
+  bool has_drive = StartsWithDriveLetter(path);
+  bool is_device_path = IsDevicePath(path, &path);
+
+  if (!has_drive && !is_device_path && !nt_path)
+    return ERROR_INVALID_NAME;
+
+  bool added_implied_device = false;
+  if (!has_drive) {
+    if (base::win::GetVersion() >= base::win::VERSION_WIN7) {
+      path = base::string16(kNTDotPrefix) + path;
+      added_implied_device = true;
+    } else {
+      return ERROR_INVALID_NAME;
+    }
+  }
+
   base::string16::size_type last_pos = base::string16::npos;
+  bool passed_once = false;
 
   do {
     path = path.substr(0, last_pos);
@@ -107,6 +175,10 @@ DWORD IsReparsePoint(const base::string16& full_path, bool* result) {
           error != ERROR_PATH_NOT_FOUND &&
           error != ERROR_INVALID_NAME) {
         // Unexpected error.
+        if (passed_once && added_implied_device &&
+            path.rfind(L'\\') == kNTDotPrefixLen - 1) {

[cpu_(ooo_6.6-7.5), 2015/02/17 21:59:45]

I get nervous when I see && == and - in a line with no ( ), I hope this is not a
operator precedence quiz.

[rvargas (doing something else), 2015/02/17 22:59:29]

Done.

+          break;
+        }
         NOTREACHED_NT();
         return error;
       }
@@ -116,6 +188,7 @@ DWORD IsReparsePoint(const base::string16& full_path, bool* result) {
       return ERROR_SUCCESS;
     }
 
+    passed_once = true;
     last_pos = path.rfind(L'\\');
   } while (last_pos > 2);  // Skip root dir.
 
@@ -123,20 +196,20 @@ DWORD IsReparsePoint(const base::string16& full_path, bool* result) {
   return ERROR_SUCCESS;
 }
 
-// We get a |full_path| of the form \??\c:\some\foo\bar, and the name that
+// We get a |full_path| of the forms accepted by IsReparsePoint(), and the name
 // we'll get from |handle| will be \device\harddiskvolume1\some\foo\bar.
 bool SameObject(HANDLE handle, const wchar_t* full_path) {
-  base::string16 path(full_path);
-  DCHECK_NT(!path.empty());
-
   // Check if it's a pipe.
-  if (IsPipe(path))
+  if (IsPipe(full_path))
     return true;

[cpu_(ooo_6.6-7.5), 2015/02/17 21:59:46]

two objects are the same if one of them is a pipe. 

Uhh..  

(yeah I know it is not new code)

[rvargas (doing something else), 2015/02/17 22:59:29]

Open to suggestions... Of course, the reasoning was that under PIPE no same
person would have redirections

 
   base::string16 actual_path;
   if (!GetPathFromHandle(handle, &actual_path))
     return false;
 
+  base::string16 path(full_path);
+  DCHECK_NT(!path.empty());
+
   // This may end with a backslash.
   const wchar_t kBackslash = '\\';
   if (path[path.length() - 1] == kBackslash)
@@ -146,19 +219,25 @@ bool SameObject(HANDLE handle, const wchar_t* full_path) {
   if (0 == _wcsicmp(actual_path.c_str(), path.c_str()))
     return true;
 
-  // Look for the drive letter.
-  size_t colon_pos = path.find(L':');
-  if (colon_pos == 0 || colon_pos == base::string16::npos)
-    return false;
+  bool nt_path = IsNTPath(path, &path);
+  bool has_drive = StartsWithDriveLetter(path);
+
+  if (!has_drive && nt_path) {
+    base::string16 simple_actual_path;
+    if (!IsDevicePath(actual_path, &simple_actual_path))
+      return false;
 
-  // Only one character for the drive.
-  if (colon_pos > 1 && path[colon_pos - 2] != kBackslash)
+    // Perfect match (case-insesitive check).
+    return (0 == _wcsicmp(simple_actual_path.c_str(), path.c_str()));
+  }
+
+  if (!has_drive)
     return false;
 
   // We only need 3 chars, but let's alloc a buffer for four.
   wchar_t drive[4] = {0};
   wchar_t vol_name[MAX_PATH];
-  memcpy(drive, &path[colon_pos - 1], 2 * sizeof(*drive));
+  memcpy(drive, &path[0], 2 * sizeof(*drive));
 
   // We'll get a double null terminated string.
   DWORD vol_length = ::QueryDosDeviceW(drive, vol_name, MAX_PATH);
@@ -169,7 +248,7 @@ bool SameObject(HANDLE handle, const wchar_t* full_path) {
   vol_length = static_cast<DWORD>(wcslen(vol_name));
 
   // The two paths should be the same length.
-  if (vol_length + path.size() - (colon_pos + 1) != actual_path.size())
+  if (vol_length + path.size() - 2 != actual_path.size())
     return false;
 
   // Check up to the drive letter.
@@ -177,20 +256,29 @@ bool SameObject(HANDLE handle, const wchar_t* full_path) {
     return false;
 
   // Check the path after the drive letter.
-  if (0 != _wcsicmp(&actual_path[vol_length], &path[colon_pos + 1]))
+  if (0 != _wcsicmp(&actual_path[vol_length], &path[2]))
     return false;
 
   return true;
 }

[cpu_(ooo_6.6-7.5), 2015/02/17 21:59:45]

if I might suggest, I think we need a helper here or elsewhere of the form

bool icompare(const std::string& s1, const std::string& s2, size_t len) {
   return 0 == _wcsnicmp(s1.c_str(), s2.c_str(), len);
}

possibly with ( ..., size_t start, size_t len)

[rvargas (doing something else), 2015/02/17 22:59:29]

Not sure the result is better, but done.

 
+// Paths like \Device\HarddiskVolume0\some\foo\bar are assumed to be already
+// expanded.
 bool ConvertToLongPath(const base::string16& short_path,
                        base::string16* long_path) {
   // Check if the path is a NT path.
-  bool is_nt_path = false;
-  base::string16 path = short_path;
-  if (0 == path.compare(0, kNTPrefixLen, kNTPrefix)) {
-    path = path.substr(kNTPrefixLen);
-    is_nt_path = true;
+  base::string16 path;
+  bool is_nt_path = IsNTPath(short_path, &path);
+  if (IsDevicePath(path, &path))
+    return false;

[cpu_(ooo_6.6-7.5), 2015/02/17 21:59:46]

can lines 272 and 273 be moved above 269 ?

[rvargas (doing something else), 2015/02/17 22:59:29]

Done.

+
+  bool added_implied_device = false;
+  if (!StartsWithDriveLetter(path) && is_nt_path &&
+      base::win::GetVersion() >= base::win::VERSION_WIN7) {
+    // This workaround does NOT work for before win7. The policy cannot have
+    // short names in that case.
+    path = base::string16(kNTDotPrefix) + path;
+    added_implied_device = true;
   }
 
   DWORD size = MAX_PATH;
@@ -226,6 +314,9 @@ bool ConvertToLongPath(const base::string16& short_path,
   }
 
   if (return_value != 0) {
+    if (added_implied_device)
+      RemoveImpliedDevice(&path);
+
     if (is_nt_path) {
       *long_path = kNTPrefix;
       *long_path += path;