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, 26 insertions, 28 deletions

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index ff20e2d..fee06b9 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -3321,10 +3321,10 @@ static int sctp_setsockopt_auth_chunk(struct sock *sk,
 				      char __user *optval,
 				      unsigned int optlen)
 {
-	struct net *net = sock_net(sk);
+	struct sctp_endpoint *ep = sctp_sk(sk)->ep;
 	struct sctp_authchunk val;
 
-	if (!net->sctp.auth_enable)
+	if (!ep->auth_enable)
 		return -EACCES;
 
 	if (optlen != sizeof(struct sctp_authchunk))
@@ -3341,7 +3341,7 @@ static int sctp_setsockopt_auth_chunk(struct sock *sk,
 	}
 
 	/* add this chunk id to the endpoint */
-	return sctp_auth_ep_add_chunkid(sctp_sk(sk)->ep, val.sauth_chunk);
+	return sctp_auth_ep_add_chunkid(ep, val.sauth_chunk);
 }
 
 /*
@@ -3354,12 +3354,12 @@ static int sctp_setsockopt_hmac_ident(struct sock *sk,
 				      char __user *optval,
 				      unsigned int optlen)
 {
-	struct net *net = sock_net(sk);
+	struct sctp_endpoint *ep = sctp_sk(sk)->ep;
 	struct sctp_hmacalgo *hmacs;
 	u32 idents;
 	int err;
 
-	if (!net->sctp.auth_enable)
+	if (!ep->auth_enable)
 		return -EACCES;
 
 	if (optlen < sizeof(struct sctp_hmacalgo))
@@ -3376,7 +3376,7 @@ static int sctp_setsockopt_hmac_ident(struct sock *sk,
 		goto out;
 	}
 
-	err = sctp_auth_ep_set_hmacs(sctp_sk(sk)->ep, hmacs);
+	err = sctp_auth_ep_set_hmacs(ep, hmacs);
 out:
 	kfree(hmacs);
 	return err;
@@ -3392,12 +3392,12 @@ static int sctp_setsockopt_auth_key(struct sock *sk,
 				    char __user *optval,
 				    unsigned int optlen)
 {
-	struct net *net = sock_net(sk);
+	struct sctp_endpoint *ep = sctp_sk(sk)->ep;
 	struct sctp_authkey *authkey;
 	struct sctp_association *asoc;
 	int ret;
 
-	if (!net->sctp.auth_enable)
+	if (!ep->auth_enable)
 		return -EACCES;
 
 	if (optlen <= sizeof(struct sctp_authkey))
@@ -3418,7 +3418,7 @@ static int sctp_setsockopt_auth_key(struct sock *sk,
 		goto out;
 	}
 
-	ret = sctp_auth_set_key(sctp_sk(sk)->ep, asoc, authkey);
+	ret = sctp_auth_set_key(ep, asoc, authkey);
 out:
 	kzfree(authkey);
 	return ret;
@@ -3434,11 +3434,11 @@ static int sctp_setsockopt_active_key(struct sock *sk,
 				      char __user *optval,
 				      unsigned int optlen)
 {
-	struct net *net = sock_net(sk);
+	struct sctp_endpoint *ep = sctp_sk(sk)->ep;
 	struct sctp_authkeyid val;
 	struct sctp_association *asoc;
 
-	if (!net->sctp.auth_enable)
+	if (!ep->auth_enable)
 		return -EACCES;
 
 	if (optlen != sizeof(struct sctp_authkeyid))
@@ -3450,8 +3450,7 @@ static int sctp_setsockopt_active_key(struct sock *sk,
 	if (!asoc && val.scact_assoc_id && sctp_style(sk, UDP))
 		return -EINVAL;
 
-	return sctp_auth_set_active_key(sctp_sk(sk)->ep, asoc,
-					val.scact_keynumber);
+	return sctp_auth_set_active_key(ep, asoc, val.scact_keynumber);
 }
 
 /*
@@ -3463,11 +3462,11 @@ static int sctp_setsockopt_del_key(struct sock *sk,
 				   char __user *optval,
 				   unsigned int optlen)
 {
-	struct net *net = sock_net(sk);
+	struct sctp_endpoint *ep = sctp_sk(sk)->ep;
 	struct sctp_authkeyid val;
 	struct sctp_association *asoc;
 
-	if (!net->sctp.auth_enable)
+	if (!ep->auth_enable)
 		return -EACCES;
 
 	if (optlen != sizeof(struct sctp_authkeyid))
@@ -3479,8 +3478,7 @@ static int sctp_setsockopt_del_key(struct sock *sk,
 	if (!asoc && val.scact_assoc_id && sctp_style(sk, UDP))
 		return -EINVAL;
 
-	return sctp_auth_del_key_id(sctp_sk(sk)->ep, asoc,
-				    val.scact_keynumber);
+	return sctp_auth_del_key_id(ep, asoc, val.scact_keynumber);
 
 }
 
@@ -5387,16 +5385,16 @@ static int sctp_getsockopt_maxburst(struct sock *sk, int len,
 static int sctp_getsockopt_hmac_ident(struct sock *sk, int len,
 				    char __user *optval, int __user *optlen)
 {
-	struct net *net = sock_net(sk);
+	struct sctp_endpoint *ep = sctp_sk(sk)->ep;
 	struct sctp_hmacalgo  __user *p = (void __user *)optval;
 	struct sctp_hmac_algo_param *hmacs;
 	__u16 data_len = 0;
 	u32 num_idents;
 
-	if (!net->sctp.auth_enable)
+	if (!ep->auth_enable)
 		return -EACCES;
 
-	hmacs = sctp_sk(sk)->ep->auth_hmacs_list;
+	hmacs = ep->auth_hmacs_list;
 	data_len = ntohs(hmacs->param_hdr.length) - sizeof(sctp_paramhdr_t);
 
 	if (len < sizeof(struct sctp_hmacalgo) + data_len)
@@ -5417,11 +5415,11 @@ static int sctp_getsockopt_hmac_ident(struct sock *sk, int len,
 static int sctp_getsockopt_active_key(struct sock *sk, int len,
 				    char __user *optval, int __user *optlen)
 {
-	struct net *net = sock_net(sk);
+	struct sctp_endpoint *ep = sctp_sk(sk)->ep;
 	struct sctp_authkeyid val;
 	struct sctp_association *asoc;
 
-	if (!net->sctp.auth_enable)
+	if (!ep->auth_enable)
 		return -EACCES;
 
 	if (len < sizeof(struct sctp_authkeyid))
@@ -5436,7 +5434,7 @@ static int sctp_getsockopt_active_key(struct sock *sk, int len,
 	if (asoc)
 		val.scact_keynumber = asoc->active_key_id;
 	else
-		val.scact_keynumber = sctp_sk(sk)->ep->active_key_id;
+		val.scact_keynumber = ep->active_key_id;
 
 	len = sizeof(struct sctp_authkeyid);
 	if (put_user(len, optlen))
@@ -5450,7 +5448,7 @@ static int sctp_getsockopt_active_key(struct sock *sk, int len,
 static int sctp_getsockopt_peer_auth_chunks(struct sock *sk, int len,
 				    char __user *optval, int __user *optlen)
 {
-	struct net *net = sock_net(sk);
+	struct sctp_endpoint *ep = sctp_sk(sk)->ep;
 	struct sctp_authchunks __user *p = (void __user *)optval;
 	struct sctp_authchunks val;
 	struct sctp_association *asoc;
@@ -5458,7 +5456,7 @@ static int sctp_getsockopt_peer_auth_chunks(struct sock *sk, int len,
 	u32    num_chunks = 0;
 	char __user *to;
 
-	if (!net->sctp.auth_enable)
+	if (!ep->auth_enable)
 		return -EACCES;
 
 	if (len < sizeof(struct sctp_authchunks))
@@ -5495,7 +5493,7 @@ num:
 static int sctp_getsockopt_local_auth_chunks(struct sock *sk, int len,
 				    char __user *optval, int __user *optlen)
 {
-	struct net *net = sock_net(sk);
+	struct sctp_endpoint *ep = sctp_sk(sk)->ep;
 	struct sctp_authchunks __user *p = (void __user *)optval;
 	struct sctp_authchunks val;
 	struct sctp_association *asoc;
@@ -5503,7 +5501,7 @@ static int sctp_getsockopt_local_auth_chunks(struct sock *sk, int len,
 	u32    num_chunks = 0;
 	char __user *to;
 
-	if (!net->sctp.auth_enable)
+	if (!ep->auth_enable)
 		return -EACCES;
 
 	if (len < sizeof(struct sctp_authchunks))
@@ -5520,7 +5518,7 @@ static int sctp_getsockopt_local_auth_chunks(struct sock *sk, int len,
 	if (asoc)
 		ch = (struct sctp_chunks_param *)asoc->c.auth_chunks;
 	else
-		ch = sctp_sk(sk)->ep->auth_chunk_list;
+		ch = ep->auth_chunk_list;
 
 	if (!ch)
 		goto num;