[tor-commits] [torsocks/master] Add basic interface for libc overload

[dgoulet at torproject.org]

commit 9acdf15bf1bc7de354dff59c611c44d58cfc83c3
Author: David Goulet <dgoulet at ev0ke.net>
Date:   Thu Jun 6 20:37:55 2013 -0400

    Add basic interface for libc overload
    
    Signed-off-by: David Goulet <dgoulet at ev0ke.net>
---
 src/common/compat.h |    6 ++++++
 src/lib/Makefile.am |    6 +++---
 src/lib/torsocks.c  |   50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 src/lib/torsocks.h  |   14 ++++++++++++++
 4 files changed, 73 insertions(+), 3 deletions(-)

diff --git a/src/common/compat.h b/src/common/compat.h
index 3ac4941..020fe8e 100644
--- a/src/common/compat.h
+++ b/src/common/compat.h
@@ -18,6 +18,12 @@
 #ifndef TORSOCKS_COMPAT_H
 #define TORSOCKS_COMPAT_H
 
+#if (defined(__linux__) || defined(__FreeBSD__) || defined(__darwin__))
+
+#define RTLD_NEXT	((void *) -1)
+
+#endif /* __linux__, __FreeBSD__, __darwin__ */
+
 #ifdef __linux__
 
 #include <pthread.h>
diff --git a/src/lib/Makefile.am b/src/lib/Makefile.am
index f578d3f..7a1586d 100644
--- a/src/lib/Makefile.am
+++ b/src/lib/Makefile.am
@@ -1,4 +1,5 @@
 AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_srcdir)/src -I$(builddir)
+AM_CFLAGS = -fno-strict-aliasing
 
 libdir = @libdir@/torsocks
 
@@ -11,7 +12,6 @@ lib_LTLIBRARIES = libtorsocks.la
 
 libtorsocks_la_SOURCES = torsocks.c torsocks.h
 
-libtorsocks_la_LDFLAGS = $(TORSOCKSLDFLAGS)
-
 libtorsocks_la_LIBADD = \
-		$(top_builddir)/src/common/libcommon.la
+		$(top_builddir)/src/common/libcommon.la \
+		-ldl
diff --git a/src/lib/torsocks.c b/src/lib/torsocks.c
index c0450ad..f5029e7 100644
--- a/src/lib/torsocks.c
+++ b/src/lib/torsocks.c
@@ -17,6 +17,8 @@
  * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#include <assert.h>
+#include <dlfcn.h>
 #include <stdlib.h>
 
 #include <common/defaults.h>
@@ -31,6 +33,27 @@
 static int is_suid;
 
 /*
+ * Lookup symbol in the loaded libraries of the binary.
+ *
+ * Return the function pointer or NULL on error.
+ */
+static void *find_libc_symbol(const char *symbol)
+{
+	void *fct_ptr = NULL;
+
+	assert(symbol);
+
+	fct_ptr = dlsym(RTLD_NEXT, symbol);
+	if (!fct_ptr) {
+		ERR("Unable to find %s", symbol);
+		goto end;
+	}
+
+end:
+	return fct_ptr;
+}
+
+/*
  * Initialize logging subsytem using either the default values or the one given
  * by the environment variables.
  */
@@ -85,3 +108,30 @@ static void __attribute__((constructor)) init()
 
 	init_logging();
 }
+
+/*
+ * Cleanup and exit with the given status.
+ */
+static void clean_exit(int status)
+{
+	exit(status);
+}
+
+/*
+ * Libc hijacked symbol connect(2).
+ */
+int connect(LIBC_CONNECT_SIG)
+{
+	static int (*libc_connect)(LIBC_CONNECT_SIG) = NULL;
+
+	/* Find symbol if not already set. */
+	if (!libc_connect) {
+		libc_connect = find_libc_symbol("connect");
+		if (!libc_connect) {
+			ERR("This is critical for torsocks. Exiting");
+			clean_exit(EXIT_FAILURE);
+		}
+	}
+
+	return libc_connect(_sockfd, _addr, _addrlen);
+}
diff --git a/src/lib/torsocks.h b/src/lib/torsocks.h
index 7e6eec1..122d711 100644
--- a/src/lib/torsocks.h
+++ b/src/lib/torsocks.h
@@ -22,4 +22,18 @@
 
 #include <common/compat.h>
 
+#if (defined(__linux__) || defined(__FreeBSD__) || defined(__darwin__))
+
+#include <sys/types.h>
+#include <sys/socket.h>
+
+#ifndef LIBC_CONNECT_SIG
+#define LIBC_CONNECT_SIG \
+	int _sockfd, const struct sockaddr *_addr, socklen_t _addrlen
+#endif /* LIBC_CONNECT_SIG */
+
+#else
+#error "OS not supported."
+#endif /* __linux__ , __FreeBSD__, __darwin__ */
+
 #endif /* TORSOCKS_H */