Revert "Use dlopen on libc instead of RTLD_NEXT"

This reverts commit f47125c.

The commit in question directly used the C library instead of RTLD_NEXT
whenever possible, based on some deadlock I didn't specify further in
the commit message.

I could not reproduce a deadlock like this and given that we don't have
a test case that fails with RTLD_NEXT tells me that it doesn't matter.

In addition to just reverting, I also added a small test case that I
used in order to try reproducing the aforementioned issue. Even though I
couldn't reproduce the issue, I'm adding the test anyway since we didn't
have a test case where we use multiple LD_PRELOAD wrappers that operate
on the same set of calls as ip2unix.

Signed-off-by: aszlig <[email protected]>

CHANGELOG.md

@@ -30,6 +30,7 @@ The format is based on [Keep a Changelog], and this project adheres to
 
 ### Removed
 - Badges (eg. LGTM and build status) in README and Hydra.
+- No longer prefer C library path over `RTLD_NEXT`.
 
 ## [2.1.4] - 2021-07-10
 

flake.nix

@@ -360,6 +360,7 @@
  in lib.mapAttrs (lib.const (lib.mapAttrs mkProgramTest)) {
  mariadb-php-abstract.x86_64-linux =
  tests/programs/mariadb-php-abstract.nix;
+ multiple-preload.x86_64-linux = tests/programs/multiple-preload.nix;
  rsession.x86_64-linux = tests/programs/rsession.nix;
  };
 

meson.build

@@ -2,7 +2,6 @@ project('ip2unix', 'cpp',
  default_options: ['cpp_std=c++17', 'warning_level=3'],
  meson_version: '>=0.47.0', version: '2.1.4')
 
-script_findlibc = files('scripts/findlibc.py')
 script_generrno = files('scripts/generrno.py')
 script_genoffsets = files('scripts/genoffsets.py')
 script_gensyms = files('scripts/gensyms.py')
@@ -55,13 +54,6 @@ deps = [
  cc.find_library('dl')
 ]
 
-libcpath = run_command(python, script_findlibc, cc.cmd_array(), check: false)
-if libcpath.returncode() == 0
- fullpath = libcpath.stdout()
- message('Found C library at ' + fullpath)
- lib_cflags += ['-DLIBC_PATH="' + fullpath + '"']
-endif
-
 systemd_enabled = get_option('systemd-support')
 
 if systemd_enabled

src/realcalls.cc

@@ -2,35 +2,4 @@
 #define IP2UNIX_REALCALL_EXTERN
 #include "realcalls.hh"
 
-#include <initializer_list>
-#include <memory>
-#include <mutex>
-
 std::mutex g_dlsym_mutex;
-
-DlsymHandle dlsym_handle;
-
-DlsymHandle::DlsymHandle() : handle(nullptr)
-{
- std::scoped_lock<std::mutex> lock(g_dlsym_mutex);
-
- for (const char *libname : {
-#ifdef LIBC_PATH
- LIBC_PATH,
-#endif
- "libc.so.6"
- }) {
- this->handle = dlopen(libname, RTLD_LAZY | RTLD_DEEPBIND);
- if (this->handle != nullptr) return;
- }
-
- this->handle = RTLD_NEXT;
-}
-
-DlsymHandle::~DlsymHandle()
-{
- std::scoped_lock<std::mutex> lock(g_dlsym_mutex);
-
- if (this->handle != RTLD_NEXT)
- dlclose(this->handle);
-}

src/realcalls.hh

@@ -24,24 +24,7 @@
 #define IP2UNIX_REALCALL_EXTERN extern
 #endif
 
-struct DlsymHandle
-{
- DlsymHandle();
- ~DlsymHandle();
-
- inline void *get(void) const {
- return this->handle;
- }
-
- private:
- DlsymHandle(const DlsymHandle&) = delete;
- DlsymHandle &operator=(const DlsymHandle&) = delete;
-
- void *handle;
-};
-
 extern std::mutex g_dlsym_mutex;
-extern DlsymHandle dlsym_handle;
 
 /* This namespace is here so that we can autogenerate and call wrappers for C
  * library functions in a convenient way. For example to call the wrapper for
@@ -58,7 +41,7 @@ namespace real {
  {
  g_dlsym_mutex.lock();
  if (this->fptr == nullptr) {
- void *result = dlsym(dlsym_handle.get(), Self::fname);
+ void *result = dlsym(RTLD_NEXT, Self::fname);
  if (result == nullptr) {
  LOG(FATAL) << "Loading of symbol '" << Self::fname
  << "' failed: " << strerror(errno);

tests/programs/multiple-preload.nix

@@ -0,0 +1,44 @@
+{ pkgs, ip2unix, ... }:
+
+pkgs.runCommand "multiple-preload" {
+ TSOCKS_DEBUG = 10;
+ TSOCKS_CONF_FILE = pkgs.writeText "tsocks.conf" ''
+ server = 127.0.0.2
+ '';
+
+ nativeBuildInputs = [
+ ip2unix
+ pkgs.tsocks
+ pkgs.netcat-openbsd
+
+ (pkgs.writeScriptBin "socksd" ''
+ #!${(pkgs.python3.withPackages (p: [ p.tiny-proxy ])).interpreter}
+ import anyio
+ from tiny_proxy import Socks4ProxyHandler
+
+ async def main():
+ handler = Socks4ProxyHandler()
+ listener = await anyio.create_tcp_listener()
+ await listener.serve(handler.handle)
+
+ anyio.run(main)
+ '')
+
+ (pkgs.writeScriptBin "testprog" ''
+ #!${pkgs.python3.interpreter}
+ import socket
+ with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
+ sock.connect(('1.2.3.4', 1234))
+ assert sock.recv(3) == b'foo'
+ '')
+ ];
+} ''
+ echo foo | nc -N -lU foo.sock &
+ while [ ! -e foo.sock ]; do sleep 1; done
+
+ ip2unix -r in,path=bar.sock -r out,path=foo.sock socksd &
+ while [ ! -e bar.sock ]; do sleep 1; done
+
+ ip2unix -vvvvv -r out,addr=127.0.0.2,path=bar.sock tsocks testprog
+ touch "$out"
+''