net: sctp: cache auth_enable per endpoint

Currently, it is possible to create an SCTP socket, then switch
auth_enable via sysctl setting to 1 and crash the system on connect:

Oops[#1]:
CPU: 0 PID: 0 Comm: swapper Not tainted 3.14.1-mipsgit-20140415 #1
task: ffffffff8056ce80 ti: ffffffff8055c000 task.ti: ffffffff8055c000
[...]
Call Trace:
[<ffffffff8043c4e8>] sctp_auth_asoc_set_default_hmac+0x68/0x80
[<ffffffff8042b300>] sctp_process_init+0x5e0/0x8a4
[<ffffffff8042188c>] sctp_sf_do_5_1B_init+0x234/0x34c
[<ffffffff804228c8>] sctp_do_sm+0xb4/0x1e8
[<ffffffff80425a08>] sctp_endpoint_bh_rcv+0x1c4/0x214
[<ffffffff8043af68>] sctp_rcv+0x588/0x630
[<ffffffff8043e8e8>] sctp6_rcv+0x10/0x24
[<ffffffff803acb50>] ip6_input+0x2c0/0x440
[<ffffffff8030fc00>] __netif_receive_skb_core+0x4a8/0x564
[<ffffffff80310650>] process_backlog+0xb4/0x18c
[<ffffffff80313cbc>] net_rx_action+0x12c/0x210
[<ffffffff80034254>] __do_softirq+0x17c/0x2ac
[<ffffffff800345e0>] irq_exit+0x54/0xb0
[<ffffffff800075a4>] ret_from_irq+0x0/0x4
[<ffffffff800090ec>] rm7k_wait_irqoff+0x24/0x48
[<ffffffff8005e388>] cpu_startup_entry+0xc0/0x148
[<ffffffff805a88b0>] start_kernel+0x37c/0x398
Code: dd0900b8  000330f8  0126302d <dcc60000> 50c0fff1  0047182a  a48306a0
03e00008  00000000
---[ end trace b530b0551467f2fd ]---
Kernel panic - not syncing: Fatal exception in interrupt

What happens while auth_enable=0 in that case is, that
ep->auth_hmacs is initialized to NULL in sctp_auth_init_hmacs()
when endpoint is being created.

After that point, if an admin switches over to auth_enable=1,
the machine can crash due to NULL pointer dereference during
reception of an INIT chunk. When we enter sctp_process_init()
via sctp_sf_do_5_1B_init() in order to respond to an INIT chunk,
the INIT verification succeeds and while we walk and process
all INIT params via sctp_process_param() we find that
net->sctp.auth_enable is set, therefore do not fall through,
but invoke sctp_auth_asoc_set_default_hmac() instead, and thus,
dereference what we have set to NULL during endpoint
initialization phase.

The fix is to make auth_enable immutable by caching its value
during endpoint initialization, so that its original value is
being carried along until destruction. The bug seems to originate
from the very first days.

Fix in joint work with Daniel Borkmann.

Reported-by: Joshua Kinard <kumba@gentoo.org>
Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Tested-by: Joshua Kinard <kumba@gentoo.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 15 deletions

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index 3a1767ef3201..fee5552ddf92 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -219,6 +219,7 @@ struct sctp_chunk *sctp_make_init(const struct sctp_association *asoc,
 			     gfp_t gfp, int vparam_len)
 {
 	struct net *net = sock_net(asoc->base.sk);
+	struct sctp_endpoint *ep = asoc->ep;
 	sctp_inithdr_t init;
 	union sctp_params addrs;
 	size_t chunksize;
@@ -278,7 +279,7 @@ struct sctp_chunk *sctp_make_init(const struct sctp_association *asoc,
 	chunksize += vparam_len;
 
 	/* Account for AUTH related parameters */
-	if (net->sctp.auth_enable) {
+	if (ep->auth_enable) {
 		/* Add random parameter length*/
 		chunksize += sizeof(asoc->c.auth_random);
 
@@ -363,7 +364,7 @@ struct sctp_chunk *sctp_make_init(const struct sctp_association *asoc,
 	}
 
 	/* Add SCTP-AUTH chunks to the parameter list */
-	if (net->sctp.auth_enable) {
+	if (ep->auth_enable) {
 		sctp_addto_chunk(retval, sizeof(asoc->c.auth_random),
 				 asoc->c.auth_random);
 		if (auth_hmacs)
@@ -2010,7 +2011,7 @@ static void sctp_process_ext_param(struct sctp_association *asoc,
 			/* if the peer reports AUTH, assume that he
 			 * supports AUTH.
 			 */
-			if (net->sctp.auth_enable)
+			if (asoc->ep->auth_enable)
 				asoc->peer.auth_capable = 1;
 			break;
 		case SCTP_CID_ASCONF:
@@ -2102,6 +2103,7 @@ static sctp_ierror_t sctp_process_unk_param(const struct sctp_association *asoc,
  * 	SCTP_IERROR_NO_ERROR - continue with the chunk
  */
 static sctp_ierror_t sctp_verify_param(struct net *net,
+					const struct sctp_endpoint *ep,
 					const struct sctp_association *asoc,
 					union sctp_params param,
 					sctp_cid_t cid,
@@ -2152,7 +2154,7 @@ static sctp_ierror_t sctp_verify_param(struct net *net,
 		goto fallthrough;
 
 	case SCTP_PARAM_RANDOM:
-		if (!net->sctp.auth_enable)
+		if (!ep->auth_enable)
 			goto fallthrough;
 
 		/* SCTP-AUTH: Secion 6.1
@@ -2169,7 +2171,7 @@ static sctp_ierror_t sctp_verify_param(struct net *net,
 		break;
 
 	case SCTP_PARAM_CHUNKS:
-		if (!net->sctp.auth_enable)
+		if (!ep->auth_enable)
 			goto fallthrough;
 
 		/* SCTP-AUTH: Section 3.2
@@ -2185,7 +2187,7 @@ static sctp_ierror_t sctp_verify_param(struct net *net,
 		break;
 
 	case SCTP_PARAM_HMAC_ALGO:
-		if (!net->sctp.auth_enable)
+		if (!ep->auth_enable)
 			goto fallthrough;
 
 		hmacs = (struct sctp_hmac_algo_param *)param.p;
@@ -2220,10 +2222,9 @@ fallthrough:
 }
 
 /* Verify the INIT packet before we process it.  */
-int sctp_verify_init(struct net *net, const struct sctp_association *asoc,
-		     sctp_cid_t cid,
-		     sctp_init_chunk_t *peer_init,
-		     struct sctp_chunk *chunk,
+int sctp_verify_init(struct net *net, const struct sctp_endpoint *ep,
+		     const struct sctp_association *asoc, sctp_cid_t cid,
+		     sctp_init_chunk_t *peer_init, struct sctp_chunk *chunk,
 		     struct sctp_chunk **errp)
 {
 	union sctp_params param;
@@ -2264,8 +2265,8 @@ int sctp_verify_init(struct net *net, const struct sctp_association *asoc,
 
 	/* Verify all the variable length parameters */
 	sctp_walk_params(param, peer_init, init_hdr.params) {
-
-		result = sctp_verify_param(net, asoc, param, cid, chunk, errp);
+		result = sctp_verify_param(net, ep, asoc, param, cid,
+					   chunk, errp);
 		switch (result) {
 		case SCTP_IERROR_ABORT:
 		case SCTP_IERROR_NOMEM:
@@ -2497,6 +2498,7 @@ static int sctp_process_param(struct sctp_association *asoc,
 	struct sctp_af *af;
 	union sctp_addr_param *addr_param;
 	struct sctp_transport *t;
+	struct sctp_endpoint *ep = asoc->ep;
 
 	/* We maintain all INIT parameters in network byte order all the
 	 * time.  This allows us to not worry about whether the parameters
@@ -2636,7 +2638,7 @@ do_addr_param:
 		goto fall_through;
 
 	case SCTP_PARAM_RANDOM:
-		if (!net->sctp.auth_enable)
+		if (!ep->auth_enable)
 			goto fall_through;
 
 		/* Save peer's random parameter */
@@ -2649,7 +2651,7 @@ do_addr_param:
 		break;
 
 	case SCTP_PARAM_HMAC_ALGO:
-		if (!net->sctp.auth_enable)
+		if (!ep->auth_enable)
 			goto fall_through;
 
 		/* Save peer's HMAC list */
@@ -2665,7 +2667,7 @@ do_addr_param:
 		break;
 
 	case SCTP_PARAM_CHUNKS:
-		if (!net->sctp.auth_enable)
+		if (!ep->auth_enable)
 			goto fall_through;
 
 		asoc->peer.peer_chunks = kmemdup(param.p,