debuggerd_handler: use syscall(__NR_close) instead of close.

Avoid bionic's file descriptor ownership checks by calling the close
syscall manually.

Test: debuggerd_test
Change-Id: I10af6aca0e66fe030fd7a53506ae61c87695641d

Author: jmgao

base/include/android-base/unique_fd.h

@@ -151,7 +151,8 @@ using unique_fd = unique_fd_impl<DefaultCloser>;
 #if !defined(_WIN32)
 
 // Inline functions, so that they can be used header-only.
-inline bool Pipe(unique_fd* read, unique_fd* write) {
+template <typename Closer>
+inline bool Pipe(unique_fd_impl<Closer>* read, unique_fd_impl<Closer>* write) {
   int pipefd[2];
 
 #if defined(__linux__)
@@ -175,7 +176,9 @@ inline bool Pipe(unique_fd* read, unique_fd* write) {
   return true;
 }
 
-inline bool Socketpair(int domain, int type, int protocol, unique_fd* left, unique_fd* right) {
+template <typename Closer>
+inline bool Socketpair(int domain, int type, int protocol, unique_fd_impl<Closer>* left,
+                       unique_fd_impl<Closer>* right) {
   int sockfd[2];
   if (socketpair(domain, type, protocol, sockfd) != 0) {
     return false;
@@ -185,7 +188,8 @@ inline bool Socketpair(int domain, int type, int protocol, unique_fd* left, uniq
   return true;
 }
 
-inline bool Socketpair(int type, unique_fd* left, unique_fd* right) {
+template <typename Closer>
+inline bool Socketpair(int type, unique_fd_impl<Closer>* left, unique_fd_impl<Closer>* right) {
   return Socketpair(AF_UNIX, type, 0, left, right);
 }
 

debuggerd/handler/debuggerd_handler.cpp

@@ -59,7 +59,16 @@
 #include "protocol.h"
 
 using android::base::Pipe;
-using android::base::unique_fd;
+
+// We muck with our fds in a 'thread' that doesn't share the same fd table.
+// Close fds in that thread with a raw close syscall instead of going through libc.
+struct FdsanBypassCloser {
+  static void Close(int fd) {
+    syscall(__NR_close, fd);
+  }
+};
+
+using unique_fd = android::base::unique_fd_impl<FdsanBypassCloser>;
 
 // see man(2) prctl, specifically the section about PR_GET_NAME
 #define MAX_TASK_NAME_LEN (16)
@@ -299,7 +308,8 @@ static int debuggerd_dispatch_pseudothread(void* arg) {
   debugger_thread_info* thread_info = static_cast<debugger_thread_info*>(arg);
 
   for (int i = 0; i < 1024; ++i) {
-    close(i);
+    // Don't use close to avoid bionic's file descriptor ownership checks.
+    syscall(__NR_close, i);
   }
 
   int devnull = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR));