>From 06f7ebb1dade2f0dbf872ea2bedf17cff4734bdd Mon Sep 17 00:00:00 2001
From: Olaf Kirch <okir@xxxxxxx>
Date: Thu, 6 Aug 2015 16:27:20 +0200
Subject: [PATCH] Fix memory corruption in PMAP_CALLIT code
We have seen occasional reports of a commercial security scanner
triggering crashes in rpcbind, but these were fairly elusive.
Now we finally got a usable core file showing that rpcbind crashed in
svc_dodestroy when trying to free a corrupted xprt->xp_netid pointer.
Closer inspection suggested that the pointer variable actually
contained a sockaddr_in.
Here's how I think the memory corruption happens:
- 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
where xprt is the UDP transport on which it received the
PMAP_CALLIT request.
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.
So, this explains how memory gets corrupted. Here's why that
eventually lead to a crash in svc_dodestroy.
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
The fix seems to be to make xprt_set_caller copy the caller's address
to xprt->xp_rtaddr using __rpc_set_netbuf rather than just overwrite
the netbuf.
Signed-off-by: Olaf Kirch <okir@xxxxxxx>
---
src/rpcb_svc_com.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/src/rpcb_svc_com.c b/src/rpcb_svc_com.c
index ff9ce6b..79fb3f5 100644
--- a/src/rpcb_svc_com.c
+++ b/src/rpcb_svc_com.c
@@ -1186,9 +1186,10 @@ check_rmtcalls(struct pollfd *pfds, int nfds)
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;
}
--
1.7.12.4
--
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@xxxxxxxx)
SUSE Linux GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
GF: Felix Imendörffer, Jane Smithard, Dilip Upmanyu, Graham Norton,
HRB 21284 (AG Nürnberg)
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