From: Denis Ovsienko <denis@ovsienko.info>
Date: Thu, 12 Jan 2017 13:47:50 +0000 (+0000)
Subject: CVE-2017-5483/SNMP: improve ASN.1 bounds checks
X-Git-Tag: tcpdump-4.9.0-bp~17
X-Git-Url: https://git.tcpdump.org/tcpdump/commitdiff_plain/eec1624f7be88008f519d92150ee0eb85633518b?ds=inline

CVE-2017-5483/SNMP: improve ASN.1 bounds checks

Kamil Frankowicz had found that truncated BE_STR and BE_SEQ ASN.1
elements could lead to an overread, from the source code it looked like
other ids could have this problem too. Move the checks introduced in
commit 72e501f out of the switch blocks to cover all ids by default.
This fixes GH#559 and GH#566.
---

diff --git a/print-snmp.c b/print-snmp.c
index 69b6a13f..1b096dcf 100644
--- a/print-snmp.c
+++ b/print-snmp.c
@@ -519,6 +519,7 @@ asn1_parse(netdissect_options *ndo,
 		ND_PRINT((ndo, "[id?%c/%s/%d]", *Form[form], Class[class].name, id));
 		return -1;
 	}
+	ND_TCHECK2(*p, elem->asnlen);
 
 	switch (form) {
 	case PRIMITIVE:
@@ -539,7 +540,6 @@ asn1_parse(netdissect_options *ndo,
 					ND_PRINT((ndo, "[asnlen=0]"));
 					return -1;
 				}
-				ND_TCHECK2(*p, elem->asnlen);
 				if (*p & ASN_BIT8)	/* negative */
 					data = -1;
 				for (i = elem->asnlen; i-- > 0; p++)
@@ -577,7 +577,6 @@ asn1_parse(netdissect_options *ndo,
 			case GAUGE:
 			case TIMETICKS: {
 				register uint32_t data;
-				ND_TCHECK2(*p, elem->asnlen);
 				elem->type = BE_UNS;
 				data = 0;
 				for (i = elem->asnlen; i-- > 0; p++)
@@ -588,7 +587,6 @@ asn1_parse(netdissect_options *ndo,
 
 			case COUNTER64: {
 				register uint64_t data64;
-				ND_TCHECK2(*p, elem->asnlen);
 			        elem->type = BE_UNS64;
 				data64 = 0;
 				for (i = elem->asnlen; i-- > 0; p++)
@@ -627,7 +625,6 @@ asn1_parse(netdissect_options *ndo,
 
 		default:
 			ND_PRINT((ndo, "[P/%s/%s]", Class[class].name, Class[class].Id[id]));
-			ND_TCHECK2(*p, elem->asnlen);
 			elem->type = BE_OCTET;
 			elem->data.raw = (const uint8_t *)p;
 			break;
diff --git a/tests/TESTLIST b/tests/TESTLIST
index 91c3b8a7..e8856c01 100644
--- a/tests/TESTLIST
+++ b/tests/TESTLIST
@@ -426,6 +426,10 @@ otv-heapoverflow-1	otv-heapoverflow-1.pcap		otv-heapoverflow-1.out		-t -c10
 otv-heapoverflow-2	otv-heapoverflow-2.pcap		otv-heapoverflow-2.out		-t -c10
 q933-heapoverflow-2	q933-heapoverflow-2.pcap	q933-heapoverflow-2.out		-t
 
+# bad packets from Kamil Frankowicz
+snmp-heapoverflow-1	snmp-heapoverflow-1.pcap	snmp-heapoverflow-1.out		-t
+snmp-heapoverflow-2	snmp-heapoverflow-2.pcap	snmp-heapoverflow-2.out		-t
+
 # RTP tests
 # fuzzed pcap
 rtp-seg-fault-1  rtp-seg-fault-1.pcap  rtp-seg-fault-1.out  -t -v -T rtp
diff --git a/tests/snmp-heapoverflow-1.out b/tests/snmp-heapoverflow-1.out
new file mode 100644
index 00000000..b8856074
--- /dev/null
+++ b/tests/snmp-heapoverflow-1.out
@@ -0,0 +1,21 @@
+30:30:30:30:30:30 > 30:30:30:30:30:30, ethertype Unknown (0x3030), length 808464432: 
+	0x0000:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0010:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0020:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0030:  3030                                     00
+30:30:30:30:30:30 > 30:30:30:30:30:30, ethertype Unknown (0x3030), length 808464432: 
+	0x0000:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0010:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0020:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0030:  3030                                     00
+30:30:30:30:30:30 > 30:30:30:30:30:30, ethertype Unknown (0x3030), length 808464432: 
+	0x0000:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0010:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0020:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0030:  3030                                     00
+30:30:30:30:30:30 > 30:30:30:30:30:30, ethertype Unknown (0x3030), length 808464432: 
+	0x0000:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0010:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0020:  3030 3030 3030 3030 3030 3030 3030 3030  0000000000000000
+	0x0030:  3030                                     00
+IP 48.48.48.48.12336 > 48.48.48.48.161:  [|snmp]
diff --git a/tests/snmp-heapoverflow-1.pcap b/tests/snmp-heapoverflow-1.pcap
new file mode 100644
index 00000000..83e57595
Binary files /dev/null and b/tests/snmp-heapoverflow-1.pcap differ
diff --git a/tests/snmp-heapoverflow-2.out b/tests/snmp-heapoverflow-2.out
new file mode 100644
index 00000000..98789159
--- /dev/null
+++ b/tests/snmp-heapoverflow-2.out
@@ -0,0 +1 @@
+IP 48.48.48.48.12336 > 48.48.48.48.162:  [|snmp]
diff --git a/tests/snmp-heapoverflow-2.pcap b/tests/snmp-heapoverflow-2.pcap
new file mode 100644
index 00000000..19fd2487
Binary files /dev/null and b/tests/snmp-heapoverflow-2.pcap differ