From c2a7a39daa657bf5732a2c8ac82472ef8e474d6a Mon Sep 17 00:00:00 2001
From: Alex 'AdUser' Z <ad_user@runbox.com>
Date: Wed, 24 Mar 2021 16:17:03 +1000
Subject: [PATCH] * challenge auth for csocket

---
 src/CMakeLists.txt |  4 ++--
 src/commands.c     |  5 ++++-
 src/csocket.c      | 31 ++++++++++++++++++++++++++++++-
 3 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index c4b6727..6883a6b 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -4,7 +4,7 @@ set(SOURCES "daemon.c" "strlcpy.c" "config.c" "buf.c" "log.c" "matches.c" "ipadd
   "appconfig.c" "statefile.c" "source.c" "filter.c" "backend.c" "jail.c")
 
 if (WITH_CSOCKET)
-  list(APPEND SOURCES "commands.c" "csocket.c")
+  list(APPEND SOURCES "md5.c" "commands.c" "csocket.c")
   add_definitions("-DWITH_CSOCKET")
 endif ()
 
@@ -30,7 +30,7 @@ add_executable("f2b-filter-test" ${SOURCES})
 set(SOURCES "strlcpy.c" "backend-test.c" "log.c" "config.c" "backend.c")
 add_executable("f2b-backend-test" ${SOURCES})
 
-set(SOURCES "strlcpy.c" "csocket-test.c" "log.c" "buf.c" "config.c" "commands.c" "csocket.c")
+set(SOURCES "strlcpy.c" "csocket-test.c" "log.c" "buf.c" "config.c" "commands.c" "csocket.c" "md5.c")
 add_executable("f2b-csocket-test" ${SOURCES})
 
 if (${CMAKE_SYSTEM_NAME} MATCHES "Linux")
diff --git a/src/commands.c b/src/commands.c
index b5bf862..07c64b3 100644
--- a/src/commands.c
+++ b/src/commands.c
@@ -24,7 +24,7 @@ struct cmd_desc {
     .type = CMD_AUTH,
     .argc = 2, .tokenc = 3,
     .tokens = { "auth", "<type>", "<password>", NULL },
-    .help = "Check authorization (available types is: plain)",
+    .help = "Check authorization (available types is: plain, challenge)",
   }, {
     .type = CMD_STATUS,
     .argc = 0, .tokenc = 1,
@@ -214,6 +214,9 @@ f2b_cmd_parse(f2b_cmd_t *cmd, const char *src) {
     if (cmd->argc == 3 && strcmp(cmd->args[1], "plain") == 0) {
       cmd->type = CMD_AUTH; return true;
     }
+    if (cmd->argc == 3 && strcmp(cmd->args[1], "challenge") == 0) {
+      cmd->type = CMD_AUTH; return true;
+    }
   } else if (strcmp(cmd->args[0], "log") == 0 && cmd->argc > 1) {
     if (cmd->argc == 2 && strcmp(cmd->args[1], "rotate") == 0) {
       cmd->type = CMD_LOG_ROTATE; return true;
diff --git a/src/csocket.c b/src/csocket.c
index dbcfbc0..1a89e5e 100644
--- a/src/csocket.c
+++ b/src/csocket.c
@@ -8,6 +8,7 @@
 #include "config.h"
 #include "buf.h"
 #include "log.h"
+#include "md5.h"
 #include "commands.h"
 #include "csocket.h"
 
@@ -24,6 +25,7 @@ typedef struct f2b_conn_t {
   int flags;
   const char *password;
   char peer[40]; /* remote address ipv4/ipv6 */
+  char challenge[40]; /* md5() of random string, nonce for auth */
 } f2b_conn_t;
 
 typedef struct f2b_sock_t {
@@ -73,6 +75,9 @@ f2b_conn_destroy(f2b_conn_t *conn) {
 
 bool
 f2b_conn_check_auth(f2b_conn_t *conn, f2b_cmd_t *cmd) {
+  char buf[64] = "";
+  MD5_CTX md5;
+
   assert(conn != NULL);
   assert(cmd  != NULL);
 
@@ -91,12 +96,36 @@ f2b_conn_check_auth(f2b_conn_t *conn, f2b_cmd_t *cmd) {
       } else {
         f2b_log_msg(log_error, "csocket auth failure from %s: password mismatch", conn->peer);
       }
+    } else if (strcmp(cmd->args[1], "challenge") == 0) {
+      MD5Init(&md5);
+      MD5Update(&md5, conn->challenge, strlen(conn->challenge));
+      MD5Update(&md5, conn->password, strlen(conn->password));
+      MD5Final(&md5);
+      memset(conn->challenge, 0x0, sizeof(conn->challenge)); /* reset */
+      if (strcmp(cmd->args[2], md5.string) == 0) {
+        conn->flags |= CSOCKET_CONN_AUTH_OK;
+        f2b_buf_append(&conn->send, "+ok\n", 0);
+        return true;
+      } else {
+        f2b_log_msg(log_error, "csocket auth failure from %s: password mismatch", conn->peer);
+      }
     } else {
       f2b_log_msg(log_error, "csocket auth failure from %s: unknown auth method", conn->peer);
     }
   } /* else: other command */
 
-  f2b_buf_append(&conn->send, "-unauthorized\n", 0);
+  if (!conn->challenge[0]) {
+    /* generate new nonce if empty */
+    snprintf(buf, sizeof(buf), "%08lx+%08lX", random(), random());
+    MD5Init(&md5);
+    MD5Update(&md5, buf, strlen(buf));
+    MD5Final(&md5);
+    strlcpy(conn->challenge, md5.string, sizeof(conn->challenge));
+  }
+
+  f2b_buf_append(&conn->send, "-unauthorized: ", 0);
+  f2b_buf_append(&conn->send, conn->challenge, 0);
+  f2b_buf_append(&conn->send, "\n", 0);
   return false;
 }