[lldb-dev] Trying to use socketpair for lldb-server fails

[Demi Obenour via lldb-dev]

To avoid a local privilage escalation, I am trying to patch LLDB not to
use a TCP socket for local communication.

The attached patch failed.  Would anyone be able to provide suggestions
for how to debug the problem?

Sincerely,

Demi
Index: source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
===
--- source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp  (revision 
308480)
+++ source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp  (working copy)
@@ -3289,7 +3289,8 @@
   }
   return error;
 }
-#if defined(__APPLE__)
+#ifndef _WIN32
+//#ifdef __APPLE__
 #define USE_SOCKETPAIR_FOR_LOCAL_CONNECTION 1
 #endif
 
Index: tools/lldb-server/lldb-gdbserver.cpp
===
--- tools/lldb-server/lldb-gdbserver.cpp(revision 308480)
+++ tools/lldb-server/lldb-gdbserver.cpp(working copy)
@@ -97,6 +97,7 @@
 {"attach", required_argument, NULL, 'a'},
 {"named-pipe", required_argument, NULL, 'N'},
 {"pipe", required_argument, NULL, 'U'},
+{"fd", required_argument, NULL, 'F'},
 {"native-regs", no_argument, NULL,
  'r'}, // Specify to use the native registers instead of the gdb defaults
// for the architecture.  NOTE: this is a do-nothing arg as it's
@@ -232,7 +233,8 @@
  GDBRemoteCommunicationServerLLGS &gdb_server,
  bool reverse_connect, const char *const host_and_port,
  const char *const progname, const char *const subcommand,
- const char *const named_pipe_path, int unnamed_pipe_fd) {
+ const char *const named_pipe_path, int unnamed_pipe_fd,
+ int connection_fd) {
   Status error;
 
   if (host_and_port && host_and_port[0]) {
@@ -257,7 +259,24 @@
 
 std::unique_ptr connection_up;
 
-if (reverse_connect) {
+if (connection_fd != -1) {
+  abort();
+  char connection_url[512];
+  snprintf(connection_url, sizeof(connection_url), "fd://%d", 
connection_fd);
+  connection_up.reset(new ConnectionFileDescriptor);
+  auto connection_result = connection_up->Connect(connection_url, &error);
+  if (connection_result != eConnectionStatusSuccess) {
+fprintf(stderr, "error: failed to connect to client at '%s' "
+"(connection status: %d)",
+connection_url, static_cast(connection_result));
+exit(-1);
+  }
+  if (error.Fail()) {
+fprintf(stderr, "error: failed to connect to client at '%s': %s",
+connection_url, error.AsCString());
+exit(-1);
+  }
+} else if (reverse_connect) {
   // llgs will connect to the gdb-remote client.
 
   // Ensure we have a port number for the connection.
@@ -364,6 +383,7 @@
   log_channels; // e.g. "lldb process threads:gdb-remote default:linux all"
   int unnamed_pipe_fd = -1;
   bool reverse_connect = false;
+  int connection_fd = -1;
 
   // ProcessLaunchInfo launch_info;
   ProcessAttachInfo attach_info;
@@ -413,6 +433,11 @@
   reverse_connect = true;
   break;
 
+case 'F':
+  if (optarg && optarg[0])
+connection_fd = StringConvert::ToUInt32(optarg, -1);
+  break;
+
 #ifndef _WIN32
 case 'S':
   // Put llgs into a new session. Terminals group processes
@@ -501,7 +526,7 @@
 
   ConnectToRemote(mainloop, gdb_server, reverse_connect, host_and_port,
   progname, subcommand, named_pipe_path.c_str(),
-  unnamed_pipe_fd);
+  unnamed_pipe_fd, connection_fd);
 
   if (!gdb_server.IsConnected()) {
 fprintf(stderr, "no connection information provided, unable to run\n");
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Re: [lldb-dev] Trying to use socketpair for lldb-server fails

[Demi Obenour via lldb-dev]

Sadly, that gives me nothing in the log file.  Also,
ConnectionFileDescriptor::Connect already seems to handle this case.

Running strace on all child processes gives a “Operation not permitted”
error from setsid().  That seems like the culprit, which is strange.

Would you mind providing the value you used for LLDB_SERVER_LOG_CHANNELS?

Demi

On Fri, Jul 21, 2017 at 2:55 PM Ted Woodward 
wrote:

> The first thing I'd do is use the lldb logging mechanism. lldb-server
> closes
> its own stdout and stderr, because nobody is interested in output from the
> server, just from the target. Except when you're debugging the server, so
> there is an easy way to turn on logging.
>
> Set the following environment variables:
> LLDB_DEBUGSERVER_LOG_FILE - this contains the path to the file the logs
> will
> be written to
> LLDB_SERVER_LOG_CHANNELS - this contains the channels and categories to
> turn
> logging on for. The format is "channel category:channel category...". If
> you
> want more than 1 category for a channel, I think "channel cat1 cat2..."
> works. This is not spelled out very clearly, unfortunately.
>
>
> Quickly glancing at the code, it looks like you need to implement a
> socketpair connection, and handling of the fd:// connection URL, starting
> in
> ConnectionFileDescriptor::Connect. The log for this would be "lldb
> connection".
>
> Ted
>
> --
> Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
> Linux Foundation Collaborative Project
>
> > -Original Message-
> > From: lldb-dev [mailto:lldb-dev-boun...@lists.llvm.org] On Behalf Of
> Demi
> > Obenour via lldb-dev
> > Sent: Wednesday, July 19, 2017 7:44 PM
> > To: lldb-dev@lists.llvm.org
> > Subject: [lldb-dev] Trying to use socketpair for lldb-server fails
> >
> > To avoid a local privilage escalation, I am trying to patch LLDB not to
> use a TCP
> > socket for local communication.
> >
> > The attached patch failed.  Would anyone be able to provide suggestions
> for
> > how to debug the problem?
> >
> > Sincerely,
> >
> > Demi
>
>
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