File 0156-erts-Fix-incorrect-UNC-path-length-calculation.patch of Package erlang

From 526bc873d91b134ffab0c484553d42a510bccd96 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20H=C3=B6gberg?= <john@erlang.org>
Date: Thu, 21 Mar 2019 17:31:47 +0100
Subject: [PATCH] erts: Fix incorrect UNC path length calculation

This didn't cause any issues for the most part since the path was
still properly formed, but it broke down when appending the
wildcards in file:list_dir/1. The ASSERT_PATH_FORMAT macro would
have caught this in no time, but it went unnoticed because we don't
run debug builds on Windows.
---
 erts/emulator/nifs/win32/win_prim_file.c | 9 ++++++---
 lib/kernel/test/file_SUITE.erl           | 3 +++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/erts/emulator/nifs/win32/win_prim_file.c b/erts/emulator/nifs/win32/win_prim_file.c
index d0aa70542f..e7d3924240 100644
--- a/erts/emulator/nifs/win32/win_prim_file.c
+++ b/erts/emulator/nifs/win32/win_prim_file.c
@@ -142,12 +142,15 @@ static posix_errno_t get_full_path(ErlNifEnv *env, WCHAR *input, efile_path_t *r
         maybe_unc_path = !sys_memcmp(result->data, L"\\\\", sizeof(WCHAR) * 2);
 
         if(maybe_unc_path && !is_long_path) {
-            /* \\localhost\c$\gurka -> \\?\UNC\localhost\c$\gurka */
+            /* \\localhost\c$\gurka -> \\?\UNC\localhost\c$\gurka
+             *
+             * Note that the length is reduced by 2 as the "\\" is replaced by
+             * the UNC prefix */
             sys_memmove(result->data + LP_UNC_PREFIX_SIZE,
                 &((WCHAR*)result->data)[2],
-                (actual_length - 1) * sizeof(WCHAR));
+                (actual_length + 1 - 2) * sizeof(WCHAR));
             sys_memcpy(result->data, LP_UNC_PREFIX, LP_UNC_PREFIX_SIZE);
-            actual_length += LP_UNC_PREFIX_LENGTH;
+            actual_length += LP_UNC_PREFIX_LENGTH - 2;
         } else if(!is_long_path) {
             /* C:\gurka -> \\?\C:\gurka */
             sys_memmove(result->data + LP_PREFIX_SIZE, result->data,
diff --git a/lib/kernel/test/file_SUITE.erl b/lib/kernel/test/file_SUITE.erl
index a51025cba6..711ffccb67 100644
--- a/lib/kernel/test/file_SUITE.erl
+++ b/lib/kernel/test/file_SUITE.erl
@@ -2191,6 +2191,9 @@ unc_paths(Config) when is_list(Config) ->
             {ok, _} = file:read_file_info("C:\\Windows\\explorer.exe"),
             {ok, _} = file:read_file_info("\\\\localhost\\c$\\Windows\\explorer.exe"),
 
+            {ok, Files} = file:list_dir("C:\\Windows\\"),
+            {ok, Files} = file:list_dir("\\\\localhost\\c$\\Windows\\"),
+
             {ok, Cwd} = file:get_cwd(),
 
             try
-- 
2.16.4