CVE-2012-6536 (C, published 2013-03-15T20:55Z)
Description: value: net/xfrm/xfrm_user.c in the Linux kernel before 3.6 does not verify that the actual Netlink message length is consistent with a certain header field, which allows local users to obtain sensitive information from kernel heap memory by leveraging the CAP_NET_ADMIN capability and providing a (1) new or (2) updated state.
Severity: LOW (CVSS v3 base score: )
Weakness: CWE-200 \u2014 Exposure of Sensitive Information to an Unauthorized Actor
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
Repository: https://github.com/torvalds/linux
Files changed:
include/linux/xfrm.h
net/xfrm/xfrm_user.c
Commit message: xfrm_user: ensure user supplied esn replay window is valid

The current code fails to ensure that the netlink message actually
contains as many bytes as the header indicates. If a user creates a new
state or updates an existing one but does not supply the bytes for the
whole ESN replay window, the kernel copies random heap bytes into the
replay bitmap, the ones happen to follow the XFRMA_REPLAY_ESN_VAL
netlink attribute. This leads to following issues:

1. The replay window has random bits set confusing the replay handling
   code later on.

2. A malicious user could use this flaw to leak up to ~3.5kB of heap
   memory when she has access to the XFRM netlink interface (requires
   CAP_NET_ADMIN).

Known users of the ESN replay window are strongSwan and Steffen's
iproute2 patch (<http://patchwork.ozlabs.org/patch/85962/>). The latter
uses the interface with a bitmap supplied while the former does not.
strongSwan is therefore prone to run into issue 1.

To fix both issues without breaking existing userland allow using the
XFRMA_REPLAY_ESN_VAL netlink attribute with either an empty bitmap or a
fully specified one. For the former case we initialize the in-kernel
bitmap with zero, for the latter we copy the user supplied bitmap. For
state updates the full bitmap must be supplied.

To prevent overflows in the bitmap length calculation the maximum size
of bmp_len is limited to 128 by this patch -- resulting in a maximum
replay window of 4096 packets. This should be sufficient for all real
life scenarios (RFC 4303 recommends a default replay window size of 64).

Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Martin Willi <martin@revosec.ch>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>


Vulnerable code:
	if ((p->flags & XFRM_STATE_ESN) && !rt)
		return -EINVAL;
	if (xfrm_replay_state_esn_len(replay_esn) !=
			xfrm_replay_state_esn_len(up))
	p = kmemdup(up, xfrm_replay_state_esn_len(up), GFP_KERNEL);
	pp = kmemdup(up, xfrm_replay_state_esn_len(up), GFP_KERNEL);

Fixed code:
#define XFRMA_REPLAY_ESN_MAX	4096

	struct xfrm_replay_state_esn *rs;
	if (p->flags & XFRM_STATE_ESN) {
		if (!rt)
			return -EINVAL;

		rs = nla_data(rt);

		if (rs->bmp_len > XFRMA_REPLAY_ESN_MAX / sizeof(rs->bmp[0]) / 8)
			return -EINVAL;

		if (nla_len(rt) < xfrm_replay_state_esn_len(rs) &&
		    nla_len(rt) != sizeof(*rs))
			return -EINVAL;
	}
	int ulen;
	ulen = xfrm_replay_state_esn_len(up);
	if (nla_len(rp) < ulen || xfrm_replay_state_esn_len(replay_esn) != ulen)
	int klen, ulen;
	klen = xfrm_replay_state_esn_len(up);
	ulen = nla_len(rta) >= klen ? klen : sizeof(*up);
	p = kzalloc(klen, GFP_KERNEL);
	pp = kzalloc(klen, GFP_KERNEL);
	memcpy(p, up, ulen);
	memcpy(pp, up, ulen);