Resolver: make inet_dns decode ugly truncated reply

Bugfix: a DNS reply with the truncation bit set containing
misleading section length (i.e header claimed length greater
than what was actually in the reply section) in the header
caused decode error in inet_dns.

1 files changed, 22 insertions, 12 deletions

diff --git a/lib/kernel/src/inet_dns.erl b/lib/kernel/src/inet_dns.erl
index 669a361c9d..20a9c8055f 100644
--- a/lib/kernel/src/inet_dns.erl
+++ b/lib/kernel/src/inet_dns.erl
@@ -129,27 +129,33 @@ do_decode(<<Id:16,
 	   RA:1,PR:1,_:2,Rcode:4,
 	   QdCount:16,AnCount:16,NsCount:16,ArCount:16,
 	   QdBuf/binary>>=Buffer) ->
-    {AnBuf,QdList} = decode_query_section(QdBuf,QdCount,Buffer),
-    {NsBuf,AnList} = decode_rr_section(AnBuf,AnCount,Buffer),
-    {ArBuf,NsList} = decode_rr_section(NsBuf,NsCount,Buffer),
-    {Rest,ArList} = decode_rr_section(ArBuf,ArCount,Buffer),
+    {AnBuf,QdList,QdTC} = decode_query_section(QdBuf,QdCount,Buffer),
+    {NsBuf,AnList,AnTC} = decode_rr_section(AnBuf,AnCount,Buffer),
+    {ArBuf,NsList,NsTC} = decode_rr_section(NsBuf,NsCount,Buffer),
+    {Rest,ArList,ArTC} = decode_rr_section(ArBuf,ArCount,Buffer),
 	case Rest of
 	    <<>> ->
+		HdrTC = decode_boolean(TC),
 		DnsHdr =
 		    #dns_header{id=Id,
 				qr=decode_boolean(QR),
 				opcode=decode_opcode(Opcode),
 				aa=decode_boolean(AA),
-				tc=decode_boolean(TC),
+				tc=HdrTC,
 				rd=decode_boolean(RD),
 				ra=decode_boolean(RA),
 				pr=decode_boolean(PR),
 				rcode=Rcode},
-		#dns_rec{header=DnsHdr,
-			 qdlist=QdList,
-			 anlist=AnList,
-			 nslist=NsList,
-			 arlist=ArList};
+		case QdTC or AnTC or NsTC or ArTC of
+		    true when not HdrTC ->
+			throw(?DECODE_ERROR);
+		    _ ->
+			#dns_rec{header=DnsHdr,
+				 qdlist=QdList,
+				 anlist=AnList,
+				 nslist=NsList,
+				 arlist=ArList}
+		end;
 	    _ ->
 		%% Garbage data after DNS message
 		throw(?DECODE_ERROR)
@@ -161,8 +167,10 @@ do_decode(_) ->
 decode_query_section(Bin, N, Buffer) ->
     decode_query_section(Bin, N, Buffer, []).
 
+decode_query_section(<<>>=Rest, N, _Buffer, Qs) ->
+    {Rest,reverse(Qs),N =/= 0};
 decode_query_section(Rest, 0, _Buffer, Qs) ->
-    {Rest,reverse(Qs)};
+    {Rest,reverse(Qs),false};
 decode_query_section(Bin, N, Buffer, Qs) ->
     case decode_name(Bin, Buffer) of
 	{<<Type:16,Class:16,Rest/binary>>,Name} ->
@@ -179,8 +187,10 @@ decode_query_section(Bin, N, Buffer, Qs) ->
 decode_rr_section(Bin, N, Buffer) ->
     decode_rr_section(Bin, N, Buffer, []).
 
+decode_rr_section(<<>>=Rest, N, _Buffer, RRs) ->
+    {Rest,reverse(RRs),N =/= 0};
 decode_rr_section(Rest, 0, _Buffer, RRs) ->
-    {Rest,reverse(RRs)};
+    {Rest,reverse(RRs),false};
 decode_rr_section(Bin, N, Buffer, RRs) ->
     case decode_name(Bin, Buffer) of
 	{<<T:16/unsigned,C:16/unsigned,TTL:4/binary,