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Date: Fri, 18 Sep 2015 15:19:12 +0200
From: Olaf Kirch <okir@...e.com>
To: oss-security@...ts.openwall.com
Cc: Steve Dickson <SteveD@...hat.com>,
 Marcus Meissner <meissner@...e.de>
Subject: Re: Re: CVE Request: remote triggerable use-after-free in rpcbind


Hi Steve,

On Thursday 17 September 2015 22:12:29 Steve Dickson wrote:
> In Olaf's patch there is a call to __rpc_set_netbuf() which is
> not visible in the upstream libtirpc lib... Did  Olaf roll his own
>  or changed libtirpc to make it visible?

Originally, I was going to use the one from libtirpc. But then I 
reconsidered because it's too ugly, and inlined a copy of it. See the 
attached patch which I submitted to SLES.

Regards,
Olaf
-- 
It is better to keep your mouth closed and let people think you are a
fool than to open it and remove all doubt.     -- Mark Twain
--------------------------------------------
Olaf Kirch - Director SUSE Linux Enterprise; R&D (okir@...e.com)
SUSE Linux GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG 
Nürnberg) 

commit 06f7ebb1dade2f0dbf872ea2bedf17cff4734bdd
Author: Olaf Kirch <okir@...e.de>
Date:   Thu Aug 6 16:27:20 2015 +0200

    Fix memory corruption in PMAP_CALLIT code
    
     - A PMAP_CALLIT call comes in on IPv4 UDP
     - rpcbind duplicates the caller's address to a netbuf and stores it in
       FINFO[0].caller_addr. caller_addr->buf now points to a memory region A
       with a size of 16 bytes
     - rpcbind forwards the call to the local service, receives a reply
     - when processing the reply, it does this in xprt_set_caller:
         xprt->xp_rtaddr = *FINFO[0].caller_addr
       It sends out the reply, and then frees the netbuf caller_addr and
       caller_addr.buf.
       However, it does not clear xp_rtaddr, so xp_rtaddr.buf now refers
       to memory region A, which is free.
     - When the next call comes in on the UDP/IPv4 socket, svc_dg_recv will
       be called, which will set xp_rtaddr to the client's address.
       It will reuse the buffer inside xp_rtaddr, ie it will write a
       sockaddr_in to region A
    
    Some time down the road, an incoming TCP connection is accepted,
    allocating a fresh SVCXPRT. The memory region A is inside the
    new SVCXPRT
    
     - While processing the TCP call, another UDP call comes in, again
       overwriting region A with the client's address
     - TCP client closes connection. In svc_destroy, we now trip over
       the garbage left in region A
    
    We ran into the case where a commercial scanner was triggering
    occasional rpcbind segfaults. The core file that was captured showed
    a corrupted xprt->xp_netid pointer that was really a sockaddr_in.
    
    Signed-off-by: Olaf Kirch <okir@...e.de>

---
 src/rpcb_svc_com.c |   23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

Index: rpcbind-0.1.6+git20080930/src/rpcb_svc_com.c
===================================================================
--- rpcbind-0.1.6+git20080930.orig/src/rpcb_svc_com.c
+++ rpcbind-0.1.6+git20080930/src/rpcb_svc_com.c
@@ -1298,12 +1298,33 @@ check_rmtcalls(struct pollfd *pfds, int
 	return (ncallbacks_found);
 }
 
+/*
+ * This is really a helper function defined in libtirpc, but unfortunately, it hasn't
+ * been exported yet.
+ */
+static struct netbuf *
+__rpc_set_netbuf(struct netbuf *nb, const void *ptr, size_t len)
+{
+	if (nb->len != len) {
+		if (nb->len)
+			mem_free(nb->buf, nb->len);
+		nb->buf = mem_alloc(len);
+		if (nb->buf == NULL)
+			return NULL;
+
+		nb->maxlen = nb->len = len;
+	}
+	memcpy(nb->buf, ptr, len);
+	return nb;
+}
+
 static void
 xprt_set_caller(SVCXPRT *xprt, struct finfo *fi)
 {
+	const struct netbuf *caller = fi->caller_addr;
 	u_int32_t *xidp;
 
-	*(svc_getrpccaller(xprt)) = *(fi->caller_addr);
+	__rpc_set_netbuf(svc_getrpccaller(xprt), caller->buf, caller->len);
 	xidp = __rpcb_get_dg_xidp(xprt);
 	*xidp = fi->caller_xid;
 }

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