[Filesystem] Fixing SVACE issue 423267

Preventing integer overflow during subtraction.

Change-Id: I5ea92045a0b3b12641cba8c05de914f71997dae9

diff --git a/src/filesystem/filesystem_instance.cc b/src/filesystem/filesystem_instance.cc
index ffea27a..0e71a14 100644 (file)
--- a/src/filesystem/filesystem_instance.cc
+++ b/src/filesystem/filesystem_instance.cc
@@ -335,13 +335,15 @@ static std::vector<std::uint8_t> read_file(std::string path, long offset = 0,
     }
   };
 
-  if (0 != offset && 0 != std::fseek(file, offset, SEEK_SET)) {
+  auto size = file_size(file);
+  if (offset < 0 || size <= (size_t)offset ||
+      (0 != offset && 0 != std::fseek(file, offset, SEEK_SET))) {
     std::string err_msg = std::string("Cannot perform seek. ") + GetErrorString(errno);
     throw std::system_error{errno, std::generic_category(), err_msg};
   }
 
   if (NPOS == length) {
-    length = file_size(file) - offset;
+    length = size - offset;
   }
 
   return read_file(file, length);