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>

diff --git a/include/linux/xfrm.h b/include/linux/xfrm.h
index 22e61fdf75a2bd46a656e164e046a006acd43343..28e493b5b94c9ba6d946d728a0908c84e34294db 100644 (file)
--- a/include/linux/xfrm.h
+++ b/include/linux/xfrm.h
@@ -84,6 +84,8 @@ struct xfrm_replay_state {
        __u32   bitmap;
 };
 
+#define XFRMA_REPLAY_ESN_MAX   4096
+
 struct xfrm_replay_state_esn {
        unsigned int    bmp_len;
        __u32           oseq;

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 8024b3dea8c2d824d1e37a3cf5f51401cb586b47..5927065e97cf9747965475175f268311e616ec82 100644 (file)
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -123,9 +123,21 @@ 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 (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;
+       }
 
        if (!rt)
                return 0;
@@ -370,14 +382,15 @@ static inline int xfrm_replay_verify_len(struct xfrm_replay_state_esn *replay_es
                                         struct nlattr *rp)
 {
        struct xfrm_replay_state_esn *up;
+       int 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 +401,28 @@ 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;
+       int 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;