Avoid signed integer overflow when calculating filesizes for VMS's ftp listings.

net/ftp/ftp_directory_listing_parser_vms.cc

 // Copyright (c) 2012 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 "net/ftp/ftp_directory_listing_parser_vms.h"
 
 #include <vector>
 
+#include "base/numerics/safe_math.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/time/time.h"
 #include "net/ftp/ftp_directory_listing_parser.h"
 #include "net/ftp/ftp_util.h"
 
 namespace net {
 
@@ skipping 29 matching lines @@
   if (base::EqualsASCII(filename_parts[1], "DIR")) {
     *parsed_filename = base::ToLowerASCII(filename_parts[0]);
     *type = FtpDirectoryListingEntry::DIRECTORY;
   } else {
     *parsed_filename = base::ToLowerASCII(listing_parts[0]);
     *type = FtpDirectoryListingEntry::FILE;
   }
   return true;
 }
 
+// VMS's directory listing gives file size in blocks. The exact file size is
+// unknown both because it is measured in blocks, but also because the block
+// size is unknown (but assumed to be 512 bytes).
+bool ApproximateFilesizeFromBlockCount(int64_t num_blocks, int64_t* out_size) {
+  if (num_blocks < 0)
+    return false;
+
+  const int kBlockSize = 512;
+  base::CheckedNumeric<int64_t> num_bytes = num_blocks;
+  num_bytes *= kBlockSize;
+
+  if (!num_bytes.IsValid())
+    return false;  // Block count is too large.
+
+  *out_size = num_bytes.ValueOrDie();
+  return true;
+}
+
 bool ParseVmsFilesize(const base::string16& input, int64_t* size) {
   if (base::ContainsOnlyChars(input, base::ASCIIToUTF16("*"))) {
     // Response consisting of asterisks means unknown size.
     *size = -1;
     return true;
   }
 
-  // VMS's directory listing gives us file size in blocks. We assume that
-  // the block size is 512 bytes. It doesn't give accurate file size, but is the
-  // best information we have.
-  const int kBlockSize = 512;
-
-  if (base::StringToInt64(input, size)) {
-    if (*size < 0)
-      return false;
-    *size *= kBlockSize;
-    return true;
-  }
+  int64_t num_blocks;
+  if (base::StringToInt64(input, &num_blocks))
+    return ApproximateFilesizeFromBlockCount(num_blocks, size);
 
   std::vector<base::StringPiece16> parts =
       base::SplitStringPiece(input, base::ASCIIToUTF16("/"),
                              base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
   if (parts.size() != 2)
     return false;
 
   int64_t blocks_used, blocks_allocated;
   if (!base::StringToInt64(parts[0], &blocks_used))
     return false;
   if (!base::StringToInt64(parts[1], &blocks_allocated))
     return false;
   if (blocks_used > blocks_allocated)
     return false;
   if (blocks_used < 0 || blocks_allocated < 0)
     return false;
 
-  *size = blocks_used * kBlockSize;
-  return true;
+  return ApproximateFilesizeFromBlockCount(blocks_used, size);
 }
 
 bool LooksLikeVmsFileProtectionListingPart(const base::string16& input) {
   if (input.length() > 4)
     return false;
 
   // On VMS there are four different permission bits: Read, Write, Execute,
   // and Delete. They appear in that order in the permission listing.
   std::string pattern("RWED");
   base::string16 match(input);
@@ skipping 189 matching lines @@
     entries->push_back(entry);
   }
 
   // The only place where we return true is after receiving the "Total" line,
   // that should be present in every VMS listing. Alternatively, if the listing
   // contains error messages, it's OK not to have the "Total" line.
   return seen_error;
 }
 
 }  // namespace net