CVE-2014-3673 (published 2014-11-10T11:55Z)

The SCTP implementation in the Linux kernel through 3.17.2 allows remote attackers to cause a denial of service (system crash) via a malformed ASCONF chunk, related to net/sctp/sm_make_chunk.c and net/sctp/sm_statefuns.c.

Severity: HIGH
CVSS v2 base score: 7.8 (AV:N/AC:L/Au:N/C:N/I:N/A:C)
CVSS v3 base score: 7.5, HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Weakness information:
cwe_id: CWE-20
cwe_name: Improper Input Validation
description: The product receives input or data, but it does
        not validate or incorrectly validates that the input has the
        properties that are required to process the data safely and
        correctly.
extended_description: 
	   Input validation is a frequently-used technique
	   for checking potentially dangerous inputs in order to
	   ensure that the inputs are safe for processing within the
	   code, or when communicating with other components.  When
	   software does not validate input properly, an attacker is
	   able to craft the input in a form that is not expected by
	   the rest of the application. This will lead to parts of the
	   system receiving unintended input, which may result in
	   altered control flow, arbitrary control of a resource, or
	   arbitrary code execution.
	   Input validation is not the only technique for
	   processing input, however.  Other techniques attempt to
	   transform potentially-dangerous input into something safe, such
	   as filtering (CWE-790) - which attempts to remove dangerous
	   inputs - or encoding/escaping (CWE-116), which attempts to
	   ensure that the input is not misinterpreted when it is included
	   in output to another component. Other techniques exist as well
	   (see CWE-138 for more examples.)
	   Input validation can be applied to:
	   
	     raw data - strings, numbers, parameters, file contents, etc.
	     metadata - information about the raw data, such as headers or size
	   
	   Data can be simple or structured.  Structured data
	   can be composed of many nested layers, composed of
	   combinations of metadata and raw data, with other simple or
	   structured data.
	   Many properties of raw data or metadata may need
	   to be validated upon entry into the code, such
	   as:
	   
	     specified quantities such as size, length, frequency, price, rate, number of operations, time, etc.
	     implied or derived quantities, such as the actual size of a file instead of a specified size
	     indexes, offsets, or positions into more complex data structures
	     symbolic keys or other elements into hash tables, associative arrays, etc.
	     well-formedness, i.e. syntactic correctness - compliance with expected syntax 
	     lexical token correctness - compliance with rules for what is treated as a token
	     specified or derived type - the actual type of the input (or what the input appears to be)
	     consistency - between individual data elements, between raw data and metadata, between references, etc.
	     conformance to domain-specific rules, e.g. business logic 
	     equivalence - ensuring that equivalent inputs are treated the same
	     authenticity, ownership, or other attestations about the input, e.g. a cryptographic signature to prove the source of the data
	   
	   Implied or derived properties of data must often
	   be calculated or inferred by the code itself.  Errors in
	   deriving properties may be considered a contributing factor
	   to improper input validation.
	   
	   Note that "input validation" has very different
	   meanings to different people, or within different
	   classification schemes.  Caution must be used when
	   referencing this CWE entry or mapping to it.  For example,
	   some weaknesses might involve inadvertently giving control
	   to an attacker over an input when they should not be able
	   to provide an input at all, but sometimes this is referred
	   to as input validation.
	   Finally, it is important to emphasize that the
	   distinctions between input validation and output escaping
	   are often blurred, and developers must be careful to
	   understand the difference, including how input validation
	   is not always sufficient to prevent vulnerabilities,
	   especially when less stringent data types must be
	   supported, such as free-form text. Consider a SQL injection
	   scenario in which a person's last name is inserted into a
	   query. The name "O'Reilly" would likely pass the validation
	   step since it is a common last name in the English
	   language. However, this valid name cannot be directly
	   inserted into the database because it contains the "'"
	   apostrophe character, which would need to be escaped or
	   otherwise transformed. In this case, removing the
	   apostrophe might reduce the risk of SQL injection, but it
	   would produce incorrect behavior because the wrong name
	   would be recorded.
       
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Daniel Borkmann
author_date: 2014-10-09 22:55:31+02:00
msg: net: sctp: fix skb_over_panic when receiving malformed ASCONF chunks

Commit 6f4c618ddb0 ("SCTP : Add paramters validity check for
ASCONF chunk") added basic verification of ASCONF chunks, however,
it is still possible to remotely crash a server by sending a
special crafted ASCONF chunk, even up to pre 2.6.12 kernels:

skb_over_panic: text:ffffffffa01ea1c3 len:31056 put:30768
 head:ffff88011bd81800 data:ffff88011bd81800 tail:0x7950
 end:0x440 dev:<NULL>
 ------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:129!
[...]
Call Trace:
 <IRQ>
 [<ffffffff8144fb1c>] skb_put+0x5c/0x70
 [<ffffffffa01ea1c3>] sctp_addto_chunk+0x63/0xd0 [sctp]
 [<ffffffffa01eadaf>] sctp_process_asconf+0x1af/0x540 [sctp]
 [<ffffffff8152d025>] ? _read_unlock_bh+0x15/0x20
 [<ffffffffa01e0038>] sctp_sf_do_asconf+0x168/0x240 [sctp]
 [<ffffffffa01e3751>] sctp_do_sm+0x71/0x1210 [sctp]
 [<ffffffff8147645d>] ? fib_rules_lookup+0xad/0xf0
 [<ffffffffa01e6b22>] ? sctp_cmp_addr_exact+0x32/0x40 [sctp]
 [<ffffffffa01e8393>] sctp_assoc_bh_rcv+0xd3/0x180 [sctp]
 [<ffffffffa01ee986>] sctp_inq_push+0x56/0x80 [sctp]
 [<ffffffffa01fcc42>] sctp_rcv+0x982/0xa10 [sctp]
 [<ffffffffa01d5123>] ? ipt_local_in_hook+0x23/0x28 [iptable_filter]
 [<ffffffff8148bdc9>] ? nf_iterate+0x69/0xb0
 [<ffffffff81496d10>] ? ip_local_deliver_finish+0x0/0x2d0
 [<ffffffff8148bf86>] ? nf_hook_slow+0x76/0x120
 [<ffffffff81496d10>] ? ip_local_deliver_finish+0x0/0x2d0
 [<ffffffff81496ded>] ip_local_deliver_finish+0xdd/0x2d0
 [<ffffffff81497078>] ip_local_deliver+0x98/0xa0
 [<ffffffff8149653d>] ip_rcv_finish+0x12d/0x440
 [<ffffffff81496ac5>] ip_rcv+0x275/0x350
 [<ffffffff8145c88b>] __netif_receive_skb+0x4ab/0x750
 [<ffffffff81460588>] netif_receive_skb+0x58/0x60

This can be triggered e.g., through a simple scripted nmap
connection scan injecting the chunk after the handshake, for
example, ...

  -------------- INIT[ASCONF; ASCONF_ACK] ------------->
  <----------- INIT-ACK[ASCONF; ASCONF_ACK] ------------
  -------------------- COOKIE-ECHO -------------------->
  <-------------------- COOKIE-ACK ---------------------
  ------------------ ASCONF; UNKNOWN ------------------>

... where ASCONF chunk of length 280 contains 2 parameters ...

  1) Add IP address parameter (param length: 16)
  2) Add/del IP address parameter (param length: 255)

... followed by an UNKNOWN chunk of e.g. 4 bytes. Here, the
Address Parameter in the ASCONF chunk is even missing, too.
This is just an example and similarly-crafted ASCONF chunks
could be used just as well.

The ASCONF chunk passes through sctp_verify_asconf() as all
parameters passed sanity checks, and after walking, we ended
up successfully at the chunk end boundary, and thus may invoke
sctp_process_asconf(). Parameter walking is done with
WORD_ROUND() to take padding into account.

In sctp_process_asconf()'s TLV processing, we may fail in
sctp_process_asconf_param() e.g., due to removal of the IP
address that is also the source address of the packet containing
the ASCONF chunk, and thus we need to add all TLVs after the
failure to our ASCONF response to remote via helper function
sctp_add_asconf_response(), which basically invokes a
sctp_addto_chunk() adding the error parameters to the given
skb.

When walking to the next parameter this time, we proceed
with ...

  length = ntohs(asconf_param->param_hdr.length);
  asconf_param = (void *)asconf_param + length;

... instead of the WORD_ROUND()'ed length, thus resulting here
in an off-by-one that leads to reading the follow-up garbage
parameter length of 12336, and thus throwing an skb_over_panic
for the reply when trying to sctp_addto_chunk() next time,
which implicitly calls the skb_put() with that length.

Fix it by using sctp_walk_params() [ which is also used in
INIT parameter processing ] macro in the verification *and*
in ASCONF processing: it will make sure we don't spill over,
that we walk parameters WORD_ROUND()'ed. Moreover, we're being
more defensive and guard against unknown parameter types and
missized addresses.

Joint work with Vlad Yasevich.

Fixes: b896b82be4ae ("[SCTP] ADDIP: Support for processing incoming ASCONF_ACK chunks.")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Vlad Yasevich <vyasevich@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: sm.h
change_type: ModificationType.MODIFY
diff: @@ -248,9 +248,9 @@ struct sctp_chunk *sctp_make_asconf_update_ip(struct sctp_association *,
 					      int, __be16);
 struct sctp_chunk *sctp_make_asconf_set_prim(struct sctp_association *asoc,
 					     union sctp_addr *addr);
-int sctp_verify_asconf(const struct sctp_association *asoc,
-		       struct sctp_paramhdr *param_hdr, void *chunk_end,
-		       struct sctp_paramhdr **errp);
+bool sctp_verify_asconf(const struct sctp_association *asoc,
+			struct sctp_chunk *chunk, bool addr_param_needed,
+			struct sctp_paramhdr **errp);
 struct sctp_chunk *sctp_process_asconf(struct sctp_association *asoc,
 				       struct sctp_chunk *asconf);
 int sctp_process_asconf_ack(struct sctp_association *asoc,

programming_language: SQL
filename: sm_make_chunk.c
change_type: ModificationType.MODIFY
diff: @@ -3110,50 +3110,63 @@ static __be16 sctp_process_asconf_param(struct sctp_association *asoc,
 	return SCTP_ERROR_NO_ERROR;
 }
 
-/* Verify the ASCONF packet before we process it.  */
-int sctp_verify_asconf(const struct sctp_association *asoc,
-		       struct sctp_paramhdr *param_hdr, void *chunk_end,
-		       struct sctp_paramhdr **errp) {
-	sctp_addip_param_t *asconf_param;
+/* Verify the ASCONF packet before we process it. */
+bool sctp_verify_asconf(const struct sctp_association *asoc,
+			struct sctp_chunk *chunk, bool addr_param_needed,
+			struct sctp_paramhdr **errp)
+{
+	sctp_addip_chunk_t *addip = (sctp_addip_chunk_t *) chunk->chunk_hdr;
 	union sctp_params param;
-	int length, plen;
-
-	param.v = (sctp_paramhdr_t *) param_hdr;
-	while (param.v <= chunk_end - sizeof(sctp_paramhdr_t)) {
-		length = ntohs(param.p->length);
-		*errp = param.p;
+	bool addr_param_seen = false;
 
-		if (param.v > chunk_end - length ||
-		    length < sizeof(sctp_paramhdr_t))
-			return 0;
+	sctp_walk_params(param, addip, addip_hdr.params) {
+		size_t length = ntohs(param.p->length);
 
+		*errp = param.p;
 		switch (param.p->type) {
+		case SCTP_PARAM_ERR_CAUSE:
+			break;
+		case SCTP_PARAM_IPV4_ADDRESS:
+			if (length != sizeof(sctp_ipv4addr_param_t))
+				return false;
+			addr_param_seen = true;
+			break;
+		case SCTP_PARAM_IPV6_ADDRESS:
+			if (length != sizeof(sctp_ipv6addr_param_t))
+				return false;
+			addr_param_seen = true;
+			break;
 		case SCTP_PARAM_ADD_IP:
 		case SCTP_PARAM_DEL_IP:
 		case SCTP_PARAM_SET_PRIMARY:
-			asconf_param = (sctp_addip_param_t *)param.v;
-			plen = ntohs(asconf_param->param_hdr.length);
-			if (plen < sizeof(sctp_addip_param_t) +
-			    sizeof(sctp_paramhdr_t))
-				return 0;
+			/* In ASCONF chunks, these need to be first. */
+			if (addr_param_needed && !addr_param_seen)
+				return false;
+			length = ntohs(param.addip->param_hdr.length);
+			if (length < sizeof(sctp_addip_param_t) +
+				     sizeof(sctp_paramhdr_t))
+				return false;
 			break;
 		case SCTP_PARAM_SUCCESS_REPORT:
 		case SCTP_PARAM_ADAPTATION_LAYER_IND:
 			if (length != sizeof(sctp_addip_param_t))
-				return 0;
-
+				return false;
 			break;
 		default:
-			break;
+			/* This is unkown to us, reject! */
+			return false;
 		}
-
-		param.v += WORD_ROUND(length);
 	}
 
-	if (param.v != chunk_end)
-		return 0;
+	/* Remaining sanity checks. */
+	if (addr_param_needed && !addr_param_seen)
+		return false;
+	if (!addr_param_needed && addr_param_seen)
+		return false;
+	if (param.v != chunk->chunk_end)
+		return false;
 
-	return 1;
+	return true;
 }
 
 /* Process an incoming ASCONF chunk with the next expected serial no. and
@@ -3162,16 +3175,17 @@ int sctp_verify_asconf(const struct sctp_association *asoc,
 struct sctp_chunk *sctp_process_asconf(struct sctp_association *asoc,
 				       struct sctp_chunk *asconf)
 {
+	sctp_addip_chunk_t *addip = (sctp_addip_chunk_t *) asconf->chunk_hdr;
+	bool all_param_pass = true;
+	union sctp_params param;
 	sctp_addiphdr_t		*hdr;
 	union sctp_addr_param	*addr_param;
 	sctp_addip_param_t	*asconf_param;
 	struct sctp_chunk	*asconf_ack;
-
 	__be16	err_code;
 	int	length = 0;
 	int	chunk_len;
 	__u32	serial;
-	int	all_param_pass = 1;
 
 	chunk_len = ntohs(asconf->chunk_hdr->length) - sizeof(sctp_chunkhdr_t);
 	hdr = (sctp_addiphdr_t *)asconf->skb->data;
@@ -3199,9 +3213,14 @@ struct sctp_chunk *sctp_process_asconf(struct sctp_association *asoc,
 		goto done;
 
 	/* Process the TLVs contained within the ASCONF chunk. */
-	while (chunk_len > 0) {
+	sctp_walk_params(param, addip, addip_hdr.params) {
+		/* Skip preceeding address parameters. */
+		if (param.p->type == SCTP_PARAM_IPV4_ADDRESS ||
+		    param.p->type == SCTP_PARAM_IPV6_ADDRESS)
+			continue;
+
 		err_code = sctp_process_asconf_param(asoc, asconf,
-						     asconf_param);
+						     param.addip);
 		/* ADDIP 4.1 A7)
 		 * If an error response is received for a TLV parameter,
 		 * all TLVs with no response before the failed TLV are
@@ -3209,28 +3228,20 @@ struct sctp_chunk *sctp_process_asconf(struct sctp_association *asoc,
 		 * the failed response are considered unsuccessful unless
 		 * a specific success indication is present for the parameter.
 		 */
-		if (SCTP_ERROR_NO_ERROR != err_code)
-			all_param_pass = 0;
-
+		if (err_code != SCTP_ERROR_NO_ERROR)
+			all_param_pass = false;
 		if (!all_param_pass)
-			sctp_add_asconf_response(asconf_ack,
-						 asconf_param->crr_id, err_code,
-						 asconf_param);
+			sctp_add_asconf_response(asconf_ack, param.addip->crr_id,
+						 err_code, param.addip);
 
 		/* ADDIP 4.3 D11) When an endpoint receiving an ASCONF to add
 		 * an IP address sends an 'Out of Resource' in its response, it
 		 * MUST also fail any subsequent add or delete requests bundled
 		 * in the ASCONF.
 		 */
-		if (SCTP_ERROR_RSRC_LOW == err_code)
+		if (err_code == SCTP_ERROR_RSRC_LOW)
 			goto done;
-
-		/* Move to the next ASCONF param. */
-		length = ntohs(asconf_param->param_hdr.length);
-		asconf_param = (void *)asconf_param + length;
-		chunk_len -= length;
 	}
-
 done:
 	asoc->peer.addip_serial++;
 

programming_language: C
filename: sm_statefuns.c
change_type: ModificationType.MODIFY
diff: @@ -3591,9 +3591,7 @@ sctp_disposition_t sctp_sf_do_asconf(struct net *net,
 	struct sctp_chunk	*asconf_ack = NULL;
 	struct sctp_paramhdr	*err_param = NULL;
 	sctp_addiphdr_t		*hdr;
-	union sctp_addr_param	*addr_param;
 	__u32			serial;
-	int			length;
 
 	if (!sctp_vtag_verify(chunk, asoc)) {
 		sctp_add_cmd_sf(commands, SCTP_CMD_REPORT_BAD_TAG,
@@ -3618,17 +3616,8 @@ sctp_disposition_t sctp_sf_do_asconf(struct net *net,
 	hdr = (sctp_addiphdr_t *)chunk->skb->data;
 	serial = ntohl(hdr->serial);
 
-	addr_param = (union sctp_addr_param *)hdr->params;
-	length = ntohs(addr_param->p.length);
-	if (length < sizeof(sctp_paramhdr_t))
-		return sctp_sf_violation_paramlen(net, ep, asoc, type, arg,
-			   (void *)addr_param, commands);
-
 	/* Verify the ASCONF chunk before processing it. */
-	if (!sctp_verify_asconf(asoc,
-			    (sctp_paramhdr_t *)((void *)addr_param + length),
-			    (void *)chunk->chunk_end,
-			    &err_param))
+	if (!sctp_verify_asconf(asoc, chunk, true, &err_param))
 		return sctp_sf_violation_paramlen(net, ep, asoc, type, arg,
 						  (void *)err_param, commands);
 
@@ -3745,10 +3734,7 @@ sctp_disposition_t sctp_sf_do_asconf_ack(struct net *net,
 	rcvd_serial = ntohl(addip_hdr->serial);
 
 	/* Verify the ASCONF-ACK chunk before processing it. */
-	if (!sctp_verify_asconf(asoc,
-	    (sctp_paramhdr_t *)addip_hdr->params,
-	    (void *)asconf_ack->chunk_end,
-	    &err_param))
+	if (!sctp_verify_asconf(asoc, asconf_ack, false, &err_param))
 		return sctp_sf_violation_paramlen(net, ep, asoc, type, arg,
 			   (void *)err_param, commands);
 

programming_language: C