diff --git a/libc/bionic/close.cpp b/libc/bionic/close.cpp
deleted file mode 100644
index 18225f0..0000000
--- a/libc/bionic/close.cpp
+++ /dev/null
@@ -1,56 +0,0 @@
-/*
- * Copyright (C) 2015 The Android Open Source Project
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- *  * Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- *  * Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
- * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
- * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#include <errno.h>
-#include <unistd.h>
-
-extern "C" int ___close(int);
-
-int close(int fd) {
-  int rc = ___close(fd);
-  if (rc == -1 && errno == EINTR) {
-    // POSIX says that if close returns with EINTR, the fd must not be closed.
-    // Linus disagrees: http://lkml.indiana.edu/hypermail/linux/kernel/0509.1/0877.html
-    // The future POSIX solution is posix_close (http://austingroupbugs.net/view.php?id=529),
-    // with the state after EINTR being undefined, and EINPROGRESS for the case where close
-    // was interrupted by a signal but the file descriptor was actually closed.
-    // My concern with that future behavior is that it breaks existing code that assumes
-    // that close only returns -1 if it failed. Unlike other system calls, I have real
-    // difficulty even imagining a caller that would need to know that close was interrupted
-    // but succeeded. So returning EINTR is wrong (because Linux always closes) and EINPROGRESS
-    // is harmful because callers need to be rewritten to understand that EINPROGRESS isn't
-    // actually a failure, but will be reported as one.
-
-    // We don't restore errno because that would incur a cost (the TLS read) for every caller.
-    // Since callers don't know ahead of time whether close will legitimately fail, they need
-    // to have stashed the old errno value anyway if they plan on using it afterwards, so
-    // us clobbering errno here doesn't change anything in that respect.
-    return 0;
-  }
-  return rc;
-}
diff --git a/libc/bionic/dirent.cpp b/libc/bionic/dirent.cpp
index 37a2fa7..153e56a 100644
--- a/libc/bionic/dirent.cpp
+++ b/libc/bionic/dirent.cpp
@@ -36,6 +36,8 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+#include <android/fdsan.h>
+
 #include "private/bionic_fortify.h"
 #include "private/ErrnoRestorer.h"
 #include "private/ScopedPthreadMutexLocker.h"
@@ -59,12 +61,18 @@
 
 #define CHECK_DIR(d) if (d == nullptr) __fortify_fatal("%s: null DIR*", __FUNCTION__)
 
+static uint64_t __get_dir_tag(DIR* dir) {
+  return android_fdsan_create_owner_tag(ANDROID_FDSAN_OWNER_TYPE_DIR,
+                                        reinterpret_cast<uint64_t>(dir));
+}
+
 static DIR* __allocate_DIR(int fd) {
   DIR* d = reinterpret_cast<DIR*>(malloc(sizeof(DIR)));
   if (d == NULL) {
     return NULL;
   }
   d->fd_ = fd;
+  android_fdsan_exchange_owner_tag(fd, 0, __get_dir_tag(d));
   d->available_bytes_ = 0;
   d->next_ = NULL;
   d->current_pos_ = 0L;
@@ -159,8 +167,9 @@
 
   int fd = d->fd_;
   pthread_mutex_destroy(&d->mutex_);
+  int rc = android_fdsan_close_with_tag(fd, __get_dir_tag(d));
   free(d);
-  return close(fd);
+  return rc;
 }
 
 void rewinddir(DIR* d) {
diff --git a/libc/bionic/fdsan.cpp b/libc/bionic/fdsan.cpp
new file mode 100644
index 0000000..df369cc
--- /dev/null
+++ b/libc/bionic/fdsan.cpp
@@ -0,0 +1,275 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <android/fdsan.h>
+
+#include <errno.h>
+#include <inttypes.h>
+#include <stdarg.h>
+#include <stdatomic.h>
+#include <string.h>
+#include <sys/cdefs.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include <async_safe/log.h>
+#include <sys/system_properties.h>
+
+#include "private/bionic_globals.h"
+#include "pthread_internal.h"
+
+extern "C" int ___close(int fd);
+pid_t __get_cached_pid();
+
+static constexpr const char* kFdsanPropertyName = "debug.fdsan";
+
+void __libc_init_fdsan() {
+  const prop_info* pi = __system_property_find(kFdsanPropertyName);
+  if (!pi) {
+    android_fdsan_set_error_level(ANDROID_FDSAN_ERROR_LEVEL_DISABLED);
+    return;
+  }
+  __system_property_read_callback(
+      pi,
+      [](void*, const char*, const char* value, uint32_t) {
+        if (strcasecmp(value, "1") == 0 || strcasecmp(value, "fatal") == 0) {
+          android_fdsan_set_error_level(ANDROID_FDSAN_ERROR_LEVEL_FATAL);
+        } else if (strcasecmp(value, "warn") == 0) {
+          android_fdsan_set_error_level(ANDROID_FDSAN_ERROR_LEVEL_WARN_ALWAYS);
+        } else if (strcasecmp(value, "warn_once") == 0) {
+          android_fdsan_set_error_level(ANDROID_FDSAN_ERROR_LEVEL_WARN_ONCE);
+        } else {
+          if (strlen(value) != 0 && strcasecmp(value, "0") != 0) {
+            async_safe_format_log(ANDROID_LOG_ERROR, "libc",
+                                  "debug.fdsan set to unknown value '%s', disabling", value);
+          }
+          android_fdsan_set_error_level(ANDROID_FDSAN_ERROR_LEVEL_DISABLED);
+        }
+      },
+      nullptr);
+}
+
+static FdTable<128>* GetFdTable() {
+  if (!__libc_shared_globals) {
+    return nullptr;
+  }
+
+  return &__libc_shared_globals->fd_table;
+}
+
+static FdEntry* GetFdEntry(int fd) {
+  if (fd < 0) {
+    return nullptr;
+  }
+
+  auto* fd_table = GetFdTable();
+  if (!fd_table) {
+    return nullptr;
+  }
+
+  return fd_table->at(fd);
+}
+
+__printflike(1, 0) static void fdsan_error(const char* fmt, ...) {
+  auto* fd_table = GetFdTable();
+  if (!fd_table) {
+    return;
+  }
+
+  auto error_level = atomic_load(&fd_table->error_level);
+  if (error_level == ANDROID_FDSAN_ERROR_LEVEL_DISABLED) {
+    return;
+  }
+
+  // Lots of code will (sensibly) fork, blindly call close on all of their fds,
+  // and then exec. Compare our cached pid value against the real one to detect
+  // this scenario and permit it.
+  pid_t cached_pid = __get_cached_pid();
+  if (cached_pid == 0 || cached_pid != syscall(__NR_getpid)) {
+    return;
+  }
+
+  va_list va;
+  va_start(va, fmt);
+  async_safe_fatal_va_list("fdsan", fmt, va);
+  va_end(va);
+
+  switch (error_level) {
+    case ANDROID_FDSAN_ERROR_LEVEL_WARN_ONCE:
+      atomic_compare_exchange_strong(&fd_table->error_level, &error_level,
+                                     ANDROID_FDSAN_ERROR_LEVEL_DISABLED);
+      break;
+
+    case ANDROID_FDSAN_ERROR_LEVEL_FATAL:
+      abort();
+
+    case ANDROID_FDSAN_ERROR_LEVEL_DISABLED:
+    case ANDROID_FDSAN_ERROR_LEVEL_WARN_ALWAYS:
+      break;
+  }
+}
+
+uint64_t android_fdsan_create_owner_tag(android_fdsan_owner_type type, uint64_t tag) {
+  if (tag == 0) {
+    return 0;
+  }
+
+  if (__predict_false((type & 0xff) != type)) {
+    async_safe_fatal("invalid android_fdsan_owner_type value: %x", type);
+  }
+
+  uint64_t result = static_cast<uint64_t>(type) << 56;
+  uint64_t mask = (static_cast<uint64_t>(1) << 56) - 1;
+  result |= tag & mask;
+  return result;
+}
+
+static const char* __tag_to_type(uint64_t tag) {
+  uint64_t type = tag >> 56;
+  switch (type) {
+    case ANDROID_FDSAN_OWNER_TYPE_FILE:
+      return "FILE*";
+    case ANDROID_FDSAN_OWNER_TYPE_DIR:
+      return "DIR*";
+    case ANDROID_FDSAN_OWNER_TYPE_UNIQUE_FD:
+      return "unique_fd";
+    case ANDROID_FDSAN_OWNER_TYPE_FILEINPUTSTREAM:
+      return "FileInputStream";
+    case ANDROID_FDSAN_OWNER_TYPE_FILEOUTPUTSTREAM:
+      return "FileOutputStream";
+    case ANDROID_FDSAN_OWNER_TYPE_RANDOMACCESSFILE:
+      return "RandomAccessFile";
+    case ANDROID_FDSAN_OWNER_TYPE_PARCELFILEDESCRIPTOR:
+      return "ParcelFileDescriptor";
+
+    case ANDROID_FDSAN_OWNER_TYPE_GENERIC_00:
+    default:
+      return "native object of unknown type";
+
+    case ANDROID_FDSAN_OWNER_TYPE_GENERIC_FF:
+      // If bits 48 to 56 are set, this is a sign-extended generic native pointer
+      uint64_t high_bits = tag >> 48;
+      if (high_bits == (1 << 16) - 1) {
+        return "native object of unknown type";
+      }
+
+      return "Java object of unknown type";
+  }
+}
+
+static uint64_t __tag_to_owner(uint64_t tag) {
+  return tag;
+}
+
+int android_fdsan_close_with_tag(int fd, uint64_t expected_tag) {
+  FdEntry* fde = GetFdEntry(fd);
+  if (!fde) {
+    return ___close(fd);
+  }
+
+  uint64_t tag = expected_tag;
+  if (!atomic_compare_exchange_strong(&fde->close_tag, &tag, 0)) {
+    const char* expected_type = __tag_to_type(expected_tag);
+    uint64_t expected_owner = __tag_to_owner(expected_tag);
+    const char* actual_type = __tag_to_type(tag);
+    uint64_t actual_owner = __tag_to_owner(tag);
+    if (expected_tag && tag) {
+      fdsan_error("attempted to close file descriptor %d, expected to be owned by %s 0x%" PRIx64
+                  ", actually owned by %s 0x%" PRIx64,
+                  fd, expected_type, expected_owner, actual_type, actual_owner);
+    } else if (expected_tag && !tag) {
+      fdsan_error("attempted to close file descriptor %d, expected to be owned by %s 0x%" PRIx64
+                  ", actually unowned",
+                  fd, expected_type, expected_owner);
+    } else if (!expected_tag && tag) {
+      fdsan_error(
+          "attempted to close file descriptor %d, expected to be unowned, actually owned by %s "
+          "0x%" PRIx64,
+          fd, actual_type, actual_owner);
+    } else if (!expected_tag && !tag) {
+      // This should never happen: our CAS failed, but expected == actual?
+      async_safe_fatal("fdsan atomic_compare_exchange_strong failed unexpectedly");
+    }
+  }
+
+  int rc = ___close(fd);
+  // If we were expecting to close with a tag, abort on EBADF.
+  if (expected_tag && rc == -1 && errno == EBADF) {
+    fdsan_error("double-close of file descriptor %d detected", fd);
+  }
+  return rc;
+}
+
+void android_fdsan_exchange_owner_tag(int fd, uint64_t expected_tag, uint64_t new_tag) {
+  FdEntry* fde = GetFdEntry(fd);
+  if (!fde) {
+    return;
+  }
+
+  uint64_t tag = expected_tag;
+  if (!atomic_compare_exchange_strong(&fde->close_tag, &tag, new_tag)) {
+    if (expected_tag == 0) {
+      fdsan_error(
+          "failed to take ownership of already-owned file descriptor: fd %d is owned by %s "
+          "%" PRIx64,
+          fd, __tag_to_type(tag), __tag_to_owner(tag));
+    } else {
+      fdsan_error(
+          "failed to exchange ownership of unowned file descriptor: expected fd %d to be owned "
+          "by %s %" PRIx64,
+          fd, __tag_to_type(expected_tag), __tag_to_owner(expected_tag));
+    }
+  }
+}
+
+android_fdsan_error_level android_fdsan_get_error_level() {
+  auto* fd_table = GetFdTable();
+  if (!fd_table) {
+    async_safe_fatal("attempted to get fdsan error level before libc initialization?");
+  }
+
+  return fd_table->error_level;
+}
+
+android_fdsan_error_level android_fdsan_set_error_level(android_fdsan_error_level new_level) {
+  auto* fd_table = GetFdTable();
+  if (!fd_table) {
+    async_safe_fatal("attempted to get fdsan error level before libc initialization?");
+  }
+
+  return atomic_exchange(&fd_table->error_level, new_level);
+}
+
+int close(int fd) {
+  int rc = android_fdsan_close_with_tag(fd, 0);
+  if (rc == -1 && errno == EINTR) {
+    return 0;
+  }
+  return rc;
+}
diff --git a/libc/bionic/fork.cpp b/libc/bionic/fork.cpp
index 33b7343..fc00207 100644
--- a/libc/bionic/fork.cpp
+++ b/libc/bionic/fork.cpp
@@ -28,6 +28,8 @@
 
 #include <unistd.h>
 
+#include <android/fdsan.h>
+
 #include "private/bionic_defs.h"
 #include "pthread_internal.h"
 
@@ -48,6 +50,11 @@
     // Update the cached pid, since clone() will not set it directly (as
     // self->tid is updated by the kernel).
     self->set_cached_pid(gettid());
+
+    // Disable fdsan post-fork, so we don't falsely trigger on processes that
+    // fork, close all of their fds blindly, and then exec.
+    android_fdsan_set_error_level(ANDROID_FDSAN_ERROR_LEVEL_DISABLED);
+
     __bionic_atfork_run_child();
   } else {
     __bionic_atfork_run_parent();
diff --git a/libc/bionic/getpid.cpp b/libc/bionic/getpid.cpp
index 779b147..c6eb586 100644
--- a/libc/bionic/getpid.cpp
+++ b/libc/bionic/getpid.cpp
@@ -32,16 +32,22 @@
 
 extern "C" pid_t __getpid();
 
-pid_t getpid() {
+pid_t __get_cached_pid() {
   pthread_internal_t* self = __get_thread();
-
   if (__predict_true(self)) {
-    // Do we have a valid cached pid?
     pid_t cached_pid;
     if (__predict_true(self->get_cached_pid(&cached_pid))) {
       return cached_pid;
     }
   }
+  return 0;
+}
+
+pid_t getpid() {
+  pid_t cached_pid = __get_cached_pid();
+  if (__predict_true(cached_pid != 0)) {
+    return cached_pid;
+  }
 
   // We're still in the dynamic linker or we're in the middle of forking, so ask the kernel.
   // We don't know whether it's safe to update the cached value, so don't try.
diff --git a/libc/bionic/libc_init_common.cpp b/libc/bionic/libc_init_common.cpp
index 1ff6603..5c54341 100644
--- a/libc/bionic/libc_init_common.cpp
+++ b/libc/bionic/libc_init_common.cpp
@@ -56,6 +56,7 @@
 extern "C" int __system_properties_init(void);
 
 __LIBC_HIDDEN__ WriteProtected<libc_globals> __libc_globals;
+__LIBC_HIDDEN__ libc_shared_globals* __libc_shared_globals;
 
 // Not public, but well-known in the BSDs.
 const char* __progname;
@@ -75,6 +76,9 @@
   });
 }
 
+void __libc_init_shared_globals(libc_shared_globals*) {
+}
+
 #if !defined(__LP64__)
 static void __check_max_thread_id() {
   if (gettid() > 65535) {
@@ -113,6 +117,7 @@
   pthread_atfork(arc4random_fork_handler, _thread_arc4_unlock, _thread_arc4_unlock);
 
   __system_properties_init(); // Requires 'environ'.
+  __libc_init_fdsan(); // Requires system properties (for debug.fdsan).
 }
 
 __noreturn static void __early_abort(int line) {
diff --git a/libc/bionic/libc_init_dynamic.cpp b/libc/bionic/libc_init_dynamic.cpp
index 05b5535..c5606fb 100644
--- a/libc/bionic/libc_init_dynamic.cpp
+++ b/libc/bionic/libc_init_dynamic.cpp
@@ -78,6 +78,8 @@
 // protector.
 __attribute__((noinline))
 static void __libc_preinit_impl(KernelArgumentBlock& args) {
+  __libc_shared_globals = args.shared_globals;
+
   __libc_init_globals(args);
   __libc_init_common(args);
 
diff --git a/libc/bionic/libc_init_static.cpp b/libc/bionic/libc_init_static.cpp
index 038f6a7..3828def 100644
--- a/libc/bionic/libc_init_static.cpp
+++ b/libc/bionic/libc_init_static.cpp
@@ -96,6 +96,11 @@
 
   // Initializing the globals requires TLS to be available for errno.
   __libc_init_main_thread(args);
+
+  static libc_shared_globals shared_globals;
+  __libc_shared_globals = &shared_globals;
+  __libc_init_shared_globals(&shared_globals);
+
   __libc_init_globals(args);
 
   __libc_init_AT_SECURE(args);
diff --git a/libc/bionic/spawn.cpp b/libc/bionic/spawn.cpp
index fde102c..e73828f 100644
--- a/libc/bionic/spawn.cpp
+++ b/libc/bionic/spawn.cpp
@@ -35,6 +35,8 @@
 #include <string.h>
 #include <unistd.h>
 
+#include <android/fdsan.h>
+
 #include "private/ScopedSignalBlocker.h"
 #include "private/SigSetConverter.h"