linux-kernel - [PATCH v2] xfrm_user: ensure user supplied esn replay window is valid

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Message-Id: <1348122160-9586-1-git-send-email-minipli@googlemail.com>
Date:	Thu, 20 Sep 2012 08:22:40 +0200
From:	Mathias Krause <minipli@...glemail.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Steffen Klassert <steffen.klassert@...unet.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mathias Krause <minipli@...glemail.com>,
	Martin Willi <martin@...osec.ch>
Subject: [PATCH v2] 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.

While at it, fix xfrm_replay_state_esn_len() to return size_t instead of
int as it calculates a length and all users expect the return value to
be positive.

Cc: Steffen Klassert <steffen.klassert@...unet.com>
Cc: Martin Willi <martin@...osec.ch>
Cc: Ben Hutchings <bhutchings@...arflare.com>
Signed-off-by: Mathias Krause <minipli@...glemail.com>
---
v2:
- compare against klen in xfrm_alloc_replay_state_esn (suggested by Ben)
- make xfrm_replay_state_esn_len() return size_t

 include/net/xfrm.h   |    4 ++--
 net/xfrm/xfrm_user.c |   27 +++++++++++++++++++++------
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 639dd13..3f7eadd 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1621,9 +1621,9 @@ static inline int xfrm_alg_auth_len(const struct xfrm_algo_auth *alg)
 	return sizeof(*alg) + ((alg->alg_key_len + 7) / 8);
 }
 
-static inline int xfrm_replay_state_esn_len(struct xfrm_replay_state_esn *replay_esn)
+static inline size_t xfrm_replay_state_esn_len(struct xfrm_replay_state_esn *rs)
 {
-	return sizeof(*replay_esn) + replay_esn->bmp_len * sizeof(__u32);
+	return sizeof(*rs) + rs->bmp_len * sizeof(__u32);
 }
 
 #ifdef CONFIG_XFRM_MIGRATE
diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 9f1e749..44c4b98 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -123,9 +123,17 @@ static inline int verify_replay(struct xfrm_usersa_info *p,
 				struct nlattr **attrs)
 {
 	struct nlattr *rt = attrs[XFRMA_REPLAY_ESN_VAL];
+	struct xfrm_replay_state_esn *rs;
 
-	if ((p->flags & XFRM_STATE_ESN) && !rt)
-		return -EINVAL;
+	if (p->flags & XFRM_STATE_ESN) {
+		if (!rt)
+			return -EINVAL;
+
+		rs = nla_data(rt);
+		if (nla_len(rt) < xfrm_replay_state_esn_len(rs) &&
+		    nla_len(rt) != sizeof(*rs))
+			return -EINVAL;
+	}
 
 	if (!rt)
 		return 0;
@@ -370,14 +378,15 @@ static inline int xfrm_replay_verify_len(struct xfrm_replay_state_esn *replay_es
 					 struct nlattr *rp)
 {
 	struct xfrm_replay_state_esn *up;
+	size_t ulen;
 
 	if (!replay_esn || !rp)
 		return 0;
 
 	up = nla_data(rp);
+	ulen = xfrm_replay_state_esn_len(up);
 
-	if (xfrm_replay_state_esn_len(replay_esn) !=
-			xfrm_replay_state_esn_len(up))
+	if (nla_len(rp) < ulen || xfrm_replay_state_esn_len(replay_esn) != ulen)
 		return -EINVAL;
 
 	return 0;
@@ -388,22 +397,28 @@ static int xfrm_alloc_replay_state_esn(struct xfrm_replay_state_esn **replay_esn
 				       struct nlattr *rta)
 {
 	struct xfrm_replay_state_esn *p, *pp, *up;
+	size_t klen, ulen;
 
 	if (!rta)
 		return 0;
 
 	up = nla_data(rta);
+	klen = xfrm_replay_state_esn_len(up);
+	ulen = nla_len(rta) >= klen ? klen : sizeof(*up);
 
-	p = kmemdup(up, xfrm_replay_state_esn_len(up), GFP_KERNEL);
+	p = kzalloc(klen, GFP_KERNEL);
 	if (!p)
 		return -ENOMEM;
 
-	pp = kmemdup(up, xfrm_replay_state_esn_len(up), GFP_KERNEL);
+	pp = kzalloc(klen, GFP_KERNEL);
 	if (!pp) {
 		kfree(p);
 		return -ENOMEM;
 	}
 
+	memcpy(p, up, ulen);
+	memcpy(pp, up, ulen);
+
 	*replay_esn = p;
 	*preplay_esn = pp;
 
-- 
1.7.10.4

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