Add a histogram to measure how often we generate NTLM hashes that are locale dependent.

The goal of this histogram isn't to measure which version the server is
expecting, but rather to upper bound how many differences (success OR failure)
there _could_ be if we changed to a locale-insensitive uppercasing approach.

Bug: 1051924
Change-Id: I8ed7471a6270b95e3cd1a4d8c808d23339321a02
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2438258Reviewed-by: David Schinazi <dschinazi@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812219}

net/ntlm/ntlm.cc

@@ -8,7 +8,9 @@
 
 #include "base/check_op.h"
 #include "base/containers/span.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/notreached.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "net/base/net_string_util.h"
 #include "net/ntlm/ntlm_buffer_writer.h"
@@ -296,6 +298,15 @@ void GenerateNtlmHashV2(const base::string16& domain,
   bool result = ToUpper(username, &upper_username);
   DCHECK(result);
 
+  // TODO(https://crbug.com/1051924): Using a locale-sensitive upper casing
+  // algorithm is problematic. A more predictable approach is to only uppercase
+  // ASCII characters, so the hash does not change depending on the user's
+  // locale. Histogram how often the locale-sensitive ToUpper() gives a result
+  // that differs from ASCII uppercasing, to see how often this ambiguity arises
+  // in practice.
+  UMA_HISTOGRAM_BOOLEAN("Net.Ntlm.HashDependsOnLocale",
+                        upper_username != base::ToUpperASCII(username));
+
   uint8_t v1_hash[kNtlmHashLen];
   GenerateNtlmHashV1(password, v1_hash);
   NtlmBufferWriter input_writer((upper_username.length() + domain.length()) *

tools/metrics/histograms/histograms_xml/net/histograms.xml

@@ -1811,6 +1811,20 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Net.Ntlm.HashDependsOnLocale" enum="Boolean"
+    expires_after="M90">
+  <owner>eroman@chromium.org</owner>
+  <owner>src/net/OWNERS</owner>
+  <summary>
+    Whether the NTLM hash depends on the user's current locale. More
+    specifically, this measures whether a locale-sensitive uppercasing of the
+    username gives a different result from an ASCII-only uppercasing. The spec
+    doesn't define uppercasing rules for NTLM. This histogram is intended to
+    inform https://crbug.com/1051924 on how often an ambiguity would arise
+    should we switch to an ASCII-only approach.
+  </summary>
+</histogram>
+
 <histogram name="Net.NumQuicSessionsAtShutdown" units="units"
     expires_after="2021-05-11">
   <owner>dschinazi@chromium.org</owner>