Fix anomalies in epmd not yet reported as security issues

Use erts_(v)snprintf to ensure no buffer overruns in debug printouts.
Disallow everything except port and name requests from remote nodes.
Disallow kill command even from localhost if alive nodes exist.
  -relaxed_command_check when starting epmd returns the possibility to
  kill this epmd when nodes are alive (from localhost).
Disallow stop command completely except if -relaxed_command_check is given
  when epmd was started.
Environment variable ERL_EPMD_RELAXED_COMMAND_CHECK can be set to always get
  -relaxed_command_check.

Author: bufflig

erts/epmd/src/Makefile.in

@@ -1,7 +1,7 @@
 #
 # %CopyrightBegin%
 # 
-# Copyright Ericsson AB 1998-2009. All Rights Reserved.
+# Copyright Ericsson AB 1998-2010. All Rights Reserved.
 # 
 # The contents of this file are subject to the Erlang Public License,
 # Version 1.1, (the "License"); you may not use this file except in
@@ -49,15 +49,27 @@ include ../epmd.mk
 
 BINDIR  = $(ERL_TOP)/bin/$(TARGET)
 OBJDIR  = $(ERL_TOP)/erts/obj$(TYPEMARKER)/$(TARGET)
+ERTS_INCL = -I$(ERL_TOP)/erts/include \
+            -I$(ERL_TOP)/erts/include/$(TARGET) \
+            -I$(ERL_TOP)/erts/include/internal \
+            -I$(ERL_TOP)/erts/include/internal/$(TARGET)
+
+# On windows we always need reentrant libraries.
+ifeq ($(TARGET),win32)
+ERTS_INTERNAL_LIBS=-L../../lib/internal/$(TARGET) -lerts_internal_r$(ERTS_LIB_TYPEMARKER) @ERTS_INTERNAL_X_LIBS@
+else
+ERTS_INTERNAL_LIBS=-L../../lib/internal/$(TARGET) -lerts_internal$(ERTS_LIB_TYPEMARKER) @ERTS_INTERNAL_X_LIBS@ -lm
+endif
 
 CC      = @CC@
 WFLAGS  = @WFLAGS@
-CFLAGS  = @CFLAGS@ @DEFS@ $(TYPE_FLAGS) $(WFLAGS)
+CFLAGS  = @CFLAGS@ @DEFS@ $(TYPE_FLAGS) $(WFLAGS) $(ERTS_INCL)
 LD      = @LD@
-LIBS    = @LIBS@
+LIBS    = @LIBS@ $(ERTS_INTERNAL_LIBS)
 LDFLAGS = @LDFLAGS@
 
 
+
 # ----------------------------------------------------
 # Release directory specification
 # ----------------------------------------------------
@@ -90,7 +102,7 @@ EPMD_OBJS = $(OBJDIR)/epmd.o       \
 #---------------------------------
 
 
-all: $(BINDIR)/$(EPMD)
+all: erts_lib $(BINDIR)/$(EPMD)
 
 docs:
 
@@ -109,9 +121,12 @@ clean:
 $(BINDIR)/$(EPMD): $(EPMD_OBJS)
 	$(PURIFY) $(LD) $(LDFLAGS) -o $@ $(EPMD_OBJS) $(LIBS)
 
-$(OBJDIR)/%.o: %.c
+$(OBJDIR)/%.o: %.c epmd.h epmd_int.h
 	$(CC) $(CFLAGS) $(EPMD_FLAGS) -o $@ -c $<
 
+erts_lib:
+	cd $(ERL_TOP)/erts/lib_src && $(MAKE) $(TYPE)
+
 include $(ERL_TOP)/make/otp_release_targets.mk
 
 release_spec: all

erts/epmd/src/epmd.c

@@ -23,6 +23,7 @@
 #endif
 #include "epmd.h"     /* Renamed from 'epmd_r4.h' */
 #include "epmd_int.h"
+#include "erl_printf.h"
 
 #ifdef HAVE_STDLIB_H
 #  include <stdlib.h>
@@ -33,6 +34,7 @@
 static void usage(EpmdVars *);
 static void run_daemon(EpmdVars*);
 static int get_port_no(void);
+static int check_relaxed(void);
 #ifdef __WIN32__
 static int has_console(void);
 #endif
@@ -161,6 +163,7 @@ int main(int argc, char** argv)
 
     g->silent         = 0; 
     g->is_daemon      = 0;
+    g->brutal_kill    = check_relaxed();
     g->packet_timeout = CLOSE_TIMEOUT; /* Default timeout */
     g->delay_accept   = 0;
     g->delay_write    = 0;
@@ -196,6 +199,9 @@ int main(int argc, char** argv)
 	} else if (strcmp(argv[0], "-daemon") == 0) {
 	    g->is_daemon = 1;
 	    argv++; argc--;
+	} else if (strcmp(argv[0], "-relaxed_command_check") == 0) {
+	    g->brutal_kill = 1;
+	    argv++; argc--;
 	} else if (strcmp(argv[0], "-kill") == 0) {
 	    if (argc == 1)
 		kill_epmd(g);
@@ -387,10 +393,10 @@ static void run_daemon(EpmdVars *g)
 
 static void usage(EpmdVars *g)
 {
-    fprintf(stderr, "usage: epmd [-d|-debug] [DbgExtra...] [-port No] [-daemon]\n");
+    fprintf(stderr, "usage: epmd [-d|-debug] [DbgExtra...] [-port No] [-daemon] [-allow_brutal_kill]\n");
     fprintf(stderr, "            [-d|-debug] [-port No] [-names|-kill|-stop name]\n\n");
-    fprintf(stderr, "See the Erlang epmd manual page for info about the usage.\n");
-    fprintf(stderr, "The -port and DbgExtra options are\n\n");
+    fprintf(stderr, "See the Erlang epmd manual page for info about the usage.\n\n");
+    fprintf(stderr, "Regular options\n");
     fprintf(stderr, "    -port No\n");
     fprintf(stderr, "        Let epmd listen to another port than default %d\n",
 	    EPMD_PORT_NO);
@@ -401,6 +407,14 @@ static void usage(EpmdVars *g)
     fprintf(stderr, "        the number of saved used node names to 5.\n\n");
     fprintf(stderr, "        If you give more than one debug flag you may\n");
     fprintf(stderr, "        get more debugging information.\n\n");
+    fprintf(stderr, "    -daemon\n");
+    fprintf(stderr, "        Start epmd detached (as a daemon)\n");
+    fprintf(stderr, "    -relaxed_command_check\n");
+    fprintf(stderr, "        Allow this instance of epmd to be killed with\n");
+    fprintf(stderr, "        epmd -kill even if there "
+	    "are registered nodes.\n");
+    fprintf(stderr, "        Also allows forced unregister (epmd -stop).\n");
+    fprintf(stderr, "\nDbgExtra options\n");
     fprintf(stderr, "    -packet_timout Seconds\n");
     fprintf(stderr, "        Set the number of seconds a connection can be\n");
     fprintf(stderr, "        inactive before epmd times out and closes the\n");
@@ -413,6 +427,18 @@ static void usage(EpmdVars *g)
     fprintf(stderr, "    -delay_write Seconds\n");
     fprintf(stderr, "        Also a simulation of a busy server. Inserts\n");
     fprintf(stderr, "        a delay before a reply is sent.\n");
+    fprintf(stderr, "\nInteractive options\n");
+    fprintf(stderr, "    -names\n");
+    fprintf(stderr, "        List names registered with the currently "
+	    "running epmd\n");
+    fprintf(stderr, "    -kill\n");
+    fprintf(stderr, "        Kill the currently runniing epmd\n");
+    fprintf(stderr, "        (only allowed if -names show empty database or\n");
+    fprintf(stderr, "        -allow_brutal_kill was given when epmd was started).\n");
+    fprintf(stderr, "    -stop Name\n");
+    fprintf(stderr, "        Forcibly unregisters a name with epmd\n");
+    fprintf(stderr, "        (only allowed if -allow_brutal_kill was given when \n");
+    fprintf(stderr, "        epmd was started).\n");
     epmd_cleanup_exit(g,1);
 }
 
@@ -432,20 +458,20 @@ static void usage(EpmdVars *g)
  *      args...      Arguments to print out according to the format
  *      
  */
-
+#define DEBUG_BUFFER_SIZE 2048
 static void dbg_gen_printf(int onsyslog,int perr,int from_level,
 			   EpmdVars *g,const char *format, va_list args)
 {
   time_t now;
   char *timestr;
-  char buf[2048];
+  char buf[DEBUG_BUFFER_SIZE];
 
   if (g->is_daemon)
     {
 #ifndef NO_SYSLOG
       if (onsyslog)
 	{
-	  vsprintf(buf, format, args);
+	  erts_vsnprintf(buf, DEBUG_BUFFER_SIZE, format, args);
 	  syslog(LOG_ERR,"epmd: %s",buf);
 	}
 #endif
@@ -456,9 +482,10 @@ static void dbg_gen_printf(int onsyslog,int perr,int from_level,
 
       time(&now);
       timestr = (char *)ctime(&now);
-      sprintf(buf, "epmd: %.*s: ", (int) strlen(timestr)-1, timestr);
+      erts_snprintf(buf, DEBUG_BUFFER_SIZE, "epmd: %.*s: ",
+		    (int) strlen(timestr)-1, timestr);
       len = strlen(buf);
-      vsprintf(buf + len, format, args);
+      erts_vsnprintf(buf + len, DEBUG_BUFFER_SIZE - len, format, args);
       if (perr == 1)
 	perror(buf);
       else
@@ -545,4 +572,9 @@ static int get_port_no(void)
     char* port_str = getenv("ERL_EPMD_PORT");
     return (port_str != NULL) ? atoi(port_str) : EPMD_PORT_NO;
 }
+static int check_relaxed(void)
+{
+    char* port_str = getenv("ERL_EPMD_RELAXED_COMMAND_CHECK");
+    return (port_str != NULL) ? 1 : 0;
+}
 

erts/epmd/src/epmd_int.h

@@ -246,8 +246,10 @@
 
 typedef struct {
   int fd;			/* File descriptor */
-  unsigned open:1;		/* TRUE if open */
-  unsigned keep:1;		/* Don't close when sent reply */
+  unsigned char open;		/* TRUE if open */
+  unsigned char keep;		/* Don't close when sent reply */
+  unsigned char local_peer;     /* The peer of this connection is via
+                                   loopback interface */
   unsigned got;			/* # of bytes we have got */
   unsigned want;		/* Number of bytes we want */
   char *buf;			/* The remaining buffer */
@@ -287,6 +289,7 @@ typedef struct {
   int debug;
   int silent; 
   int is_daemon;
+  int brutal_kill;
   unsigned packet_timeout;
   unsigned delay_accept;
   unsigned delay_write;
@@ -308,6 +311,7 @@ void epmd_call(EpmdVars*,int);
 void run(EpmdVars*);
 void epmd_cleanup_exit(EpmdVars*, int);
 int epmd_conn_close(EpmdVars*,Connection*);
+void stop_cli(EpmdVars *g, char *name);
 
 #ifdef DONT_USE_MAIN
 int  start_epmd(char *,char *,char *,char *,char *,char *,char *,char *,char *,char *);

erts/epmd/src/epmd_srv.c

@@ -386,6 +386,10 @@ static void do_request(g, fd, s, buf, bsize)
     {
     case EPMD_ALIVE2_REQ:
       dbg_printf(g,1,"** got ALIVE2_REQ");
+      if (!s->local_peer) {
+	   dbg_printf(g,0,"ALIVE2_REQ from non local address");
+	   return;
+      }
 
       /* The packet has the format "axxyyyyyy" where xx is port, given
 	 in network byte order, and yyyyyy is symname, possibly null
@@ -555,6 +559,10 @@ static void do_request(g, fd, s, buf, bsize)
 
     case EPMD_DUMP_REQ:
       dbg_printf(g,1,"** got DUMP_REQ");
+      if (!s->local_peer) {
+	   dbg_printf(g,0,"DUMP_REQ from non local address");
+	   return;
+      }
       {
 	Node *node;
 
@@ -604,7 +612,19 @@ static void do_request(g, fd, s, buf, bsize)
       break;
 
     case EPMD_KILL_REQ:
+      if (!s->local_peer) {
+	   dbg_printf(g,0,"KILL_REQ from non local address");
+	   return;
+      }
       dbg_printf(g,1,"** got KILL_REQ");
+
+      if (!g->brutal_kill && (g->nodes.reg != NULL)) {
+	  dbg_printf(g,0,"Disallowed KILL_REQ, live nodes");
+	  if (reply(g, fd,"NO",2) != 2)
+	      dbg_printf(g,0,"failed to send reply to KILL_REQ");
+	  return;
+      }
+
       if (reply(g, fd,"OK",2) != 2)
 	dbg_printf(g,0,"failed to send reply to KILL_REQ");
       dbg_tty_printf(g,1,"epmd killed");
@@ -614,6 +634,15 @@ static void do_request(g, fd, s, buf, bsize)
 
     case EPMD_STOP_REQ:
       dbg_printf(g,1,"** got STOP_REQ");
+      if (!s->local_peer) {
+	   dbg_printf(g,0,"STOP_REQ from non local address");
+	   return;
+      }
+      if (!g->brutal_kill) {
+	  dbg_printf(g,0,"Disallowed STOP_REQ, no relaxed_command_check");
+	  return;
+      }
+
       if (bsize <= 1 )
 	{
 	  dbg_printf(g,0,"packet too small for request STOP_REQ (%d)",bsize);
@@ -701,6 +730,14 @@ static int conn_open(EpmdVars *g,int fd)
 
   for (i = 0; i < g->max_conn; i++) {
     if (g->conn[i].open == EPMD_FALSE) {
+      struct sockaddr_in si;
+#ifdef HAVE_SOCKLEN_T
+      socklen_t st;
+#else
+      int st;
+#endif
+      st = sizeof(si);
+
       g->active_conn++;
       s = &g->conn[i];
 
@@ -710,6 +747,20 @@ static int conn_open(EpmdVars *g,int fd)
       s->fd   = fd;
       s->open = EPMD_TRUE;
       s->keep = EPMD_FALSE;
+
+      /* Determine if connection is from localhost */
+      if (getpeername(s->fd,(struct sockaddr*) &si,&st) ||
+	  st < sizeof(si)) {
+	  /* Failure to get peername is regarder as non local host */
+	  s->local_peer = EPMD_FALSE;
+      } else {
+	  s->local_peer =
+	      ((((unsigned) ntohl(si.sin_addr.s_addr)) & 0xFF000000U) ==
+	       0x7F000000U); /* Only 127.x.x.x allowed, no false positives */
+      }
+      dbg_tty_printf(g,2,(s->local_peer) ? "Local peer connected" :
+		     "Non-local peer connected");
+
       s->want = 0;		/* Currently unknown */
       s->got  = 0;
       s->mod_time = current_time(g); /* Note activity */