Subject: [PATCH] backport Fix write-after-free error in DHCPv6 code
 CVE-2022-0934 refers

Reference:https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=03345ecefe
---
 src/rfc3315.c | 44 +++++++++++++++++++++++++-------------------
 1 file changed, 25 insertions(+), 19 deletions(-)

diff --git a/src/rfc3315.c b/src/rfc3315.c
index 16ce2ca..cdb4b64 100644
--- a/src/rfc3315.c
+++ b/src/rfc3315.c
@@ -33,9 +33,9 @@ struct state {
   unsigned int mac_len, mac_type;
 };
 
-static int dhcp6_maybe_relay(struct state *state, void *inbuff, size_t sz, 
+static int dhcp6_maybe_relay(struct state *state, unsigned char *inbuff, size_t sz, 
 			     struct in6_addr *client_addr, int is_unicast, time_t now);
-static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_t sz, int is_unicast, time_t now);
+static int dhcp6_no_relay(struct state *state, int msg_type, unsigned char *inbuff, size_t sz, int is_unicast, time_t now);
 static void log6_opts(int nest, unsigned int xid, void *start_opts, void *end_opts);
 static void log6_packet(struct state *state, char *type, struct in6_addr *addr, char *string);
 static void log6_quiet(struct state *state, char *type, struct in6_addr *addr, char *string);
@@ -105,12 +105,12 @@ unsigned short dhcp6_reply(struct dhcp_context *context, int interface, char *if
 }
 
 /* This cost me blood to write, it will probably cost you blood to understand - srk. */
-static int dhcp6_maybe_relay(struct state *state, void *inbuff, size_t sz, 
+static int dhcp6_maybe_relay(struct state *state, unsigned char *inbuff, size_t sz, 
 			     struct in6_addr *client_addr, int is_unicast, time_t now)
 {
   void *end = inbuff + sz;
   void *opts = inbuff + 34;
-  int msg_type = *((unsigned char *)inbuff);
+  int msg_type = *inbuff;
   unsigned char *outmsgtypep;
   void *opt;
   struct dhcp_vendor *vendor;
@@ -260,15 +260,15 @@ static int dhcp6_maybe_relay(struct state *state, void *inbuff, size_t sz,
   return 1;
 }
 
-static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_t sz, int is_unicast, time_t now)
+static int dhcp6_no_relay(struct state *state, int msg_type, unsigned char *inbuff, size_t sz, int is_unicast, time_t now)
 {
   void *opt;
-  int i, o, o1, start_opts;
+  int i, o, o1, start_opts, start_msg;
   struct dhcp_opt *opt_cfg;
   struct dhcp_netid *tagif;
   struct dhcp_config *config = NULL;
   struct dhcp_netid known_id, iface_id, v6_id;
-  unsigned char *outmsgtypep;
+  unsigned char outmsgtype;
   struct dhcp_vendor *vendor;
   struct dhcp_context *context_tmp;
   struct dhcp_mac *mac_opt;
@@ -297,11 +297,12 @@ static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_
   v6_id.next = state->tags;
   state->tags = &v6_id;
 
-  /* copy over transaction-id, and save pointer to message type */
-  if (!(outmsgtypep = put_opt6(inbuff, 4)))
+  start_msg = save_counter(-1);
+  /* copy over transaction-id */
+  if (!put_opt6(inbuff, 4))
     return 0;
   start_opts = save_counter(-1);
-  state->xid = outmsgtypep[3] | outmsgtypep[2] << 8 | outmsgtypep[1] << 16;
+  state->xid = inbuff[3] | inbuff[2] << 8 | inbuff[1] << 16;
    
   /* We're going to be linking tags from all context we use. 
      mark them as unused so we don't link one twice and break the list */
@@ -348,7 +349,7 @@ static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_
       (msg_type == DHCP6REQUEST || msg_type == DHCP6RENEW || msg_type == DHCP6RELEASE || msg_type == DHCP6DECLINE))
     
     {  
-      *outmsgtypep = DHCP6REPLY;
+      outmsgtype = DHCP6REPLY;
       o1 = new_opt6(OPTION6_STATUS_CODE);
       put_opt6_short(DHCP6USEMULTI);
       put_opt6_string("Use multicast");
@@ -620,11 +621,11 @@ static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_
 	struct dhcp_netid *solicit_tags;
 	struct dhcp_context *c;
 	
-	*outmsgtypep = DHCP6ADVERTISE;
+	outmsgtype = DHCP6ADVERTISE;
 	
 	if (opt6_find(state->packet_options, state->end, OPTION6_RAPID_COMMIT, 0))
 	  {
-	    *outmsgtypep = DHCP6REPLY;
+	    outmsgtype = DHCP6REPLY;
 	    state->lease_allocate = 1;
 	    o = new_opt6(OPTION6_RAPID_COMMIT);
 	    end_opt6(o);
@@ -811,7 +812,7 @@ static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_
 	int start = save_counter(-1);
 
 	/* set reply message type */
-	*outmsgtypep = DHCP6REPLY;
+	outmsgtype = DHCP6REPLY;
 	state->lease_allocate = 1;
 
 	log6_quiet(state, "DHCPREQUEST", NULL, ignore ? _("ignored") : NULL);
@@ -926,7 +927,7 @@ static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_
 	int address_assigned = 0;
 
 	/* set reply message type */
-	*outmsgtypep = DHCP6REPLY;
+	outmsgtype = DHCP6REPLY;
 	
 	log6_quiet(state, msg_type == DHCP6RENEW ? "DHCPRENEW" : "DHCPREBIND", NULL, NULL);
 
@@ -1061,7 +1062,7 @@ static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_
 	struct dhcp_config *find_config = NULL;
 
 	/* set reply message type */
-	*outmsgtypep = DHCP6REPLY;
+	outmsgtype = DHCP6REPLY;
 	
 	log6_quiet(state, "DHCPCONFIRM", NULL, NULL);
 
@@ -1151,7 +1152,7 @@ static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_
 	log6_quiet(state, "DHCPINFORMATION-REQUEST", NULL, ignore ? _("ignored") : state->hostname);
 	if (ignore)
 	  return 0;
-	*outmsgtypep = DHCP6REPLY;
+	outmsgtype = DHCP6REPLY;
 	tagif = add_options(state, 1);
 	break;
       }
@@ -1160,7 +1161,7 @@ static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_
     case DHCP6RELEASE:
       {
 	/* set reply message type */
-	*outmsgtypep = DHCP6REPLY;
+	outmsgtype = DHCP6REPLY;
 
 	log6_quiet(state, "DHCPRELEASE", NULL, NULL);
 
@@ -1225,7 +1226,7 @@ static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_
     case DHCP6DECLINE:
       {
 	/* set reply message type */
-	*outmsgtypep = DHCP6REPLY;
+	outmsgtype = DHCP6REPLY;
 	
 	log6_quiet(state, "DHCPDECLINE", NULL, NULL);
 
@@ -1305,6 +1306,11 @@ static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_
       }
 
     }
+
+  /* Fill in the message type. Note that we store the offset,
+     not a direct pointer, since the packet memory may have been
+     reallocated */
+  ((unsigned char *)(daemon->outpacket.iov_base))[start_msg] = outmsgtype;
   
   log_tags(tagif, state->xid);
   log6_opts(0, state->xid, daemon->outpacket.iov_base + start_opts, daemon->outpacket.iov_base + save_counter(-1));
-- 
1.8.3.1