From 377d3cf830c24a8ac870628e6c8dbd0a9c908231 Mon Sep 17 00:00:00 2001
From: Harald Welte <laforge@gnumonks.org>
Date: Sun, 25 Dec 2016 17:21:29 +0100
Subject: [PATCH] add a LD_PRELOAD wrapper to trace client <-> qmuxd
 communications

---
 qmi/ld_preload_wrapper/Makefile        |  13 +++
 qmi/ld_preload_wrapper/qmuxd_wrapper.c | 127 +++++++++++++++++++++++++
 2 files changed, 140 insertions(+)
 create mode 100644 qmi/ld_preload_wrapper/Makefile
 create mode 100644 qmi/ld_preload_wrapper/qmuxd_wrapper.c

diff --git a/qmi/ld_preload_wrapper/Makefile b/qmi/ld_preload_wrapper/Makefile
new file mode 100644
index 0000000..8d42ba3
--- /dev/null
+++ b/qmi/ld_preload_wrapper/Makefile
@@ -0,0 +1,13 @@
+CFLAGS=-fPIC -Wall
+LDFLAGS=-shared -ldl
+
+all: qmuxd_wrapper.so
+
+%.o: %.c
+	$(CC) $(CFLAGS) -o $@ -c $^
+
+qmuxd_wrapper.so: qmuxd_wrapper.o
+	$(CC) $(LDFLAGS) -o $@ $^
+
+clean:
+	@rm -f qmuxd_wrapper.so *.o
diff --git a/qmi/ld_preload_wrapper/qmuxd_wrapper.c b/qmi/ld_preload_wrapper/qmuxd_wrapper.c
new file mode 100644
index 0000000..7b2830d
--- /dev/null
+++ b/qmi/ld_preload_wrapper/qmuxd_wrapper.c
@@ -0,0 +1,127 @@
+#define _GNU_SOURCE
+#include <dlfcn.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+
+static char hexd_buff[4096];
+static const char hex_chars[] = "0123456789abcdef";
+
+static char *_osmo_hexdump(const unsigned char *buf, int len, char *delim)
+{
+	int i;
+	char *cur = hexd_buff;
+
+	hexd_buff[0] = 0;
+	for (i = 0; i < len; i++) {
+		const char *delimp = delim;
+		int len_remain = sizeof(hexd_buff) - (cur - hexd_buff);
+		if (len_remain < 3)
+			break;
+
+		*cur++ = hex_chars[buf[i] >> 4];
+		*cur++ = hex_chars[buf[i] & 0xf];
+
+		while (len_remain > 1 && *delimp) {
+			*cur++ = *delimp++;
+			len_remain--;
+		}
+
+		*cur = 0;
+	}
+	hexd_buff[sizeof(hexd_buff)-1] = 0;
+	return hexd_buff;
+}
+
+static char *osmo_hexdump(const unsigned char *buf, int len)
+{
+	return _osmo_hexdump(buf, len, " ");
+}
+
+
+
+
+/* Function pointers to hold the value of the glibc functions */
+static ssize_t (*real_write)(int fd, const void *buf, size_t count);
+static ssize_t (*real_read)(int fd, void *buf, size_t count);
+static int (*real_connect)(int fd, const struct sockaddr *addr, socklen_t addrlen);
+static ssize_t (*real_send)(int sockfd, const void *buf, size_t len, int flags);
+static ssize_t (*real_recv)(int sockfd, void *buf, size_t len, int flags);
+static int (*real_close)(int fd);
+
+static int trace_fds[16]= { -1, };
+static int num_trace_fds = 0;
+
+static void dump_qmuxd(int fd, int to_qmux, const void *buf, size_t len)
+{
+	int i;
+
+	for (i = 0; i < num_trace_fds; i++) {
+		if (trace_fds[i] == fd)
+			printf("%s_qmuxd(%u, %04x): %s\n", to_qmux ? "to" : "from", fd, len, osmo_hexdump(buf, len));
+	}
+}
+
+/* wrapping write function call */
+ssize_t write(int fd, const void *buf, size_t count)
+{
+	dump_qmuxd(fd, 1, buf, count);
+
+	real_write = dlsym(RTLD_NEXT, "write");
+	return real_write(fd, buf, count);
+}
+
+ssize_t read(int fd, void *buf, size_t count)
+{
+	dump_qmuxd(fd, 0, buf, count);
+
+	real_read = dlsym(RTLD_NEXT, "read");
+	return real_read(fd, buf, count);
+}
+
+ssize_t send(int fd, const void *buf, size_t count, int flags)
+{
+	dump_qmuxd(fd, 1, buf, count);
+
+	real_send = dlsym(RTLD_NEXT, "send");
+	return real_send(fd, buf, count, flags);
+}
+
+ssize_t recv(int fd, void *buf, size_t len, int flags)
+{
+	dump_qmuxd(fd, 0, buf, len);
+
+	real_recv = dlsym(RTLD_NEXT, "recv");
+	return real_recv(fd, buf, len, flags);
+}
+
+int connect(int fd, const struct sockaddr *addr, socklen_t addrlen)
+{
+	if (addr->sa_family == AF_UNIX) {
+		struct sockaddr_un *sun = (struct sockaddr_un *)addr;
+		if (!strcmp(sun->sun_path, "/var/qmux_connect_socket")) {
+			printf("Found socketfd to qmuxd: %d\n", fd);
+			trace_fds[num_trace_fds++] = fd;
+		}
+	}
+
+	real_connect = dlsym(RTLD_NEXT, "connect");
+	return real_connect(fd, addr, addrlen);
+}
+
+int close(int fd)
+{
+	int i;
+
+	for (i = 0; i < num_trace_fds; i++) {
+		if (trace_fds[i] == fd) {
+			printf("Closed socketfd to qmuxd: %d\n", fd);
+			trace_fds[i] = -1;
+		}
+	}
+	real_close = dlsym(RTLD_NEXT, "close");
+	return real_close(fd);
+}