From b14878ccb7fac0242db82720b784ab62c467c0dc Mon Sep 17 00:00:00 2001 From: Vlad Yasevich Date: Thu, 17 Apr 2014 17:26:50 +0200 Subject: 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: [] sctp_auth_asoc_set_default_hmac+0x68/0x80 [] sctp_process_init+0x5e0/0x8a4 [] sctp_sf_do_5_1B_init+0x234/0x34c [] sctp_do_sm+0xb4/0x1e8 [] sctp_endpoint_bh_rcv+0x1c4/0x214 [] sctp_rcv+0x588/0x630 [] sctp6_rcv+0x10/0x24 [] ip6_input+0x2c0/0x440 [] __netif_receive_skb_core+0x4a8/0x564 [] process_backlog+0xb4/0x18c [] net_rx_action+0x12c/0x210 [] __do_softirq+0x17c/0x2ac [] irq_exit+0x54/0xb0 [] ret_from_irq+0x0/0x4 [] rm7k_wait_irqoff+0x24/0x48 [] cpu_startup_entry+0xc0/0x148 [] start_kernel+0x37c/0x398 Code: dd0900b8 000330f8 0126302d 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 Signed-off-by: Vlad Yasevich Signed-off-by: Daniel Borkmann Acked-by: Neil Horman Tested-by: Joshua Kinard Signed-off-by: David S. Miller --- net/sctp/endpointola.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'net/sctp/endpointola.c') diff --git a/net/sctp/endpointola.c b/net/sctp/endpointola.c index 8e5fdea05216..3d9f429858dc 100644 --- a/net/sctp/endpointola.c +++ b/net/sctp/endpointola.c @@ -68,7 +68,8 @@ static struct sctp_endpoint *sctp_endpoint_init(struct sctp_endpoint *ep, if (!ep->digest) return NULL; - if (net->sctp.auth_enable) { + ep->auth_enable = net->sctp.auth_enable; + if (ep->auth_enable) { /* Allocate space for HMACS and CHUNKS authentication * variables. There are arrays that we encode directly * into parameters to make the rest of the operations easier. -- cgit v1.2.3