Cap size of exponent when converting floats

When detecting the exponent on a floating point number, cap the maximum
amount we'll multiply by otherwise we can get excessivly large numbers.

Bug: chromium:843074
Change-Id: I6a8d1b4c20b66e305d2727f464119b1e74beb699
Reviewed-on: https://pdfium-review.googlesource.com/32570
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>

2 files changed, 22 insertions, 3 deletions

diff --git a/core/fxcrt/fx_extension.cpp b/core/fxcrt/fx_extension.cpp
index b1f2a95d62..a27e0279c6 100644
--- a/core/fxcrt/fx_extension.cpp
+++ b/core/fxcrt/fx_extension.cpp
@@ -6,13 +6,15 @@
 
 #include "core/fxcrt/fx_extension.h"
 
-#include "core/fxcrt/fx_fallthrough.h"
-
 #include <algorithm>
 #include <cwctype>
+#include <limits>
+
+#include "core/fxcrt/fx_fallthrough.h"
 
 float FXSYS_wcstof(const wchar_t* pwsStr, int32_t iLength, int32_t* pUsedLen) {
   ASSERT(pwsStr);
+
   if (iLength < 0)
     iLength = static_cast<int32_t>(wcslen(pwsStr));
   if (iLength == 0)
@@ -62,13 +64,22 @@ float FXSYS_wcstof(const wchar_t* pwsStr, int32_t iLength, int32_t* pUsedLen) {
       ++iUsedLen;
     }
 
-    size_t exp_value = 0;
+    int32_t exp_value = 0;
     while (iUsedLen < iLength) {
       wchar_t wch = pwsStr[iUsedLen];
       if (!std::iswdigit(wch))
         break;
 
       exp_value = exp_value * 10.0f + (wch - L'0');
+      // Exponent is outside the valid range, fail.
+      if ((negative_exponent &&
+           -exp_value < std::numeric_limits<float>::min_exponent10) ||
+          (!negative_exponent &&
+           exp_value > std::numeric_limits<float>::max_exponent10)) {
+        *pUsedLen = 0;
+        return 0.0f;
+      }
+
       ++iUsedLen;
     }
 
diff --git a/core/fxcrt/fx_extension_unittest.cpp b/core/fxcrt/fx_extension_unittest.cpp
index f7e07c7c65..155b7014b7 100644
--- a/core/fxcrt/fx_extension_unittest.cpp
+++ b/core/fxcrt/fx_extension_unittest.cpp
@@ -134,6 +134,14 @@ TEST(fxcrt, FXSYS_wcstof) {
   EXPECT_FLOAT_EQ(1.234e10f, FXSYS_wcstof(L"1.234E10", 8, &used_len));
   EXPECT_EQ(8, used_len);
 
+  used_len = 0;
+  EXPECT_FLOAT_EQ(0.0f, FXSYS_wcstof(L"1.234E100000000000000", 21, &used_len));
+  EXPECT_EQ(0, used_len);
+
+  used_len = 0;
+  EXPECT_FLOAT_EQ(0.0f, FXSYS_wcstof(L"1.234E-128", 21, &used_len));
+  EXPECT_EQ(0, used_len);
+
   // TODO(dsinclair): This should round as per IEEE 64-bit values.
   // EXPECT_EQ(L"123456789.01234567", FXSYS_wcstof(L"123456789.012345678"));
   used_len = 0;