Fix error handling in POSIX version of the base::File::GetLength.

base/files/memory_mapped_file_posix.cc

 // Copyright 2013 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 "base/files/memory_mapped_file.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
@@ skipping 13 matching lines @@
     const MemoryMappedFile::Region& region,
     Access access) {
   ThreadRestrictions::AssertIOAllowed();
 
   off_t map_start = 0;
   size_t map_size = 0;
   int32_t data_offset = 0;
 
   if (region == MemoryMappedFile::Region::kWholeFile) {
     int64_t file_len = file_.GetLength();
-    if (file_len == -1) {
+    if (file_len < 0) {
       DPLOG(ERROR) << "fstat " << file_.GetPlatformFile();
       return false;
     }
     map_size = static_cast<size_t>(file_len);
     length_ = map_size;
   } else {
     // The region can be arbitrarily aligned. mmap, instead, requires both the
     // start and size to be page-aligned. Hence, we map here the page-aligned
     // outer region [|aligned_start|, |aligned_start| + |size|] which contains
     // |region| and then add up the |data_offset| displacement.
@@ skipping 26 matching lines @@
     case READ_ONLY:
       flags |= PROT_READ;
       break;
     case READ_WRITE:
       flags |= PROT_READ | PROT_WRITE;
       break;
     case READ_WRITE_EXTEND:
       // POSIX won't auto-extend the file when it is written so it must first
       // be explicitly extended to the maximum size. Zeros will fill the new
       // space.
-      file_.SetLength(std::max(file_.GetLength(), region.offset + region.size));
+      auto file_len = file_.GetLength();
+      if (file_len < 0) {
+        DPLOG(ERROR) << "fstat " << file_.GetPlatformFile();
+        return false;
+      }
+      file_.SetLength(std::max(file_len, region.offset + region.size));
       flags |= PROT_READ | PROT_WRITE;
       break;
   }
   data_ = static_cast<uint8_t*>(mmap(NULL, map_size, flags, MAP_SHARED,
                                      file_.GetPlatformFile(), map_start));
   if (data_ == MAP_FAILED) {
     DPLOG(ERROR) << "mmap " << file_.GetPlatformFile();
     return false;
   }
 
   data_ += data_offset;
   return true;
 }
 #endif
 
 void MemoryMappedFile::CloseHandles() {
   ThreadRestrictions::AssertIOAllowed();
 
   if (data_ != NULL)
     munmap(data_, length_);
   file_.Close();
 
   data_ = NULL;
   length_ = 0;
 }
 
 }  // namespace base