From 19c6708bbcdc5e8f0241b567a1e55dd579d0304a Mon Sep 17 00:00:00 2001
From: Christopher Dykes <cdykes@fb.com>
Date: Thu, 25 Aug 2016 14:52:05 -0700
Subject: [PATCH] Allow locking nullptr if the length is 0

Summary:
Because apparently this is valid (and we test it).
This also adds a check in mmap to make sure we aren't passing an invalid handle to `MapViewOfFileEx`.

Reviewed By: yfeldblum

Differential Revision: D3772853

fbshipit-source-id: 11593997a3fb12b7b391c5e52661060b71341aef
---
 folly/portability/SysMman.cpp | 14 ++++++++++++++
 folly/portability/SysMman.h   |  1 +
 2 files changed, 15 insertions(+)

diff --git a/folly/portability/SysMman.cpp b/folly/portability/SysMman.cpp
index 9827f045..38d56ae3 100755
--- a/folly/portability/SysMman.cpp
+++ b/folly/portability/SysMman.cpp
@@ -64,6 +64,13 @@ int madvise(const void* addr, size_t len, int advise) {
 }
 
 int mlock(const void* addr, size_t len) {
+  // For some strange reason, it's allowed to
+  // lock a nullptr as long as length is zero.
+  // VirtualLock doesn't allow it, so handle
+  // it specially.
+  if (addr == nullptr && len == 0) {
+    return 0;
+  }
   if (!VirtualLock((void*)addr, len)) {
     return -1;
   }
@@ -106,6 +113,9 @@ void* mmap(void* addr, size_t length, int prot, int flags, int fd, off_t off) {
         (DWORD)((length >> 32) & 0xFFFFFFFF),
         (DWORD)(length & 0xFFFFFFFF),
         nullptr);
+    if (fmh == nullptr) {
+      return MAP_FAILED;
+    }
     ret = MapViewOfFileEx(
         fmh,
         accessFlags,
@@ -148,6 +158,10 @@ int mprotect(void* addr, size_t size, int prot) {
 }
 
 int munlock(const void* addr, size_t length) {
+  // See comment in mlock
+  if (addr == nullptr && length == 0) {
+    return 0;
+  }
   if (!VirtualUnlock((void*)addr, length)) {
     return -1;
   }
diff --git a/folly/portability/SysMman.h b/folly/portability/SysMman.h
index 52dd33c8..907c6778 100755
--- a/folly/portability/SysMman.h
+++ b/folly/portability/SysMman.h
@@ -44,6 +44,7 @@
 #define PROT_WRITE 2
 #define PROT_EXEC 4
 
+#define MADV_NORMAL 0
 #define MADV_DONTNEED 0
 #define MADV_SEQUENTIAL 0
 
-- 
2.34.1