[PATCH v2 net] xfrm: fix stack access out of bounds with CONFIG_XFRM_SUB_POLICY

[PATCH v2 net] xfrm: fix stack access out of bounds with CONFIG_XFRM_SUB_POLICY

[Sabrina Dubroca]

When CONFIG_XFRM_SUB_POLICY=y, xfrm_dst stores a copy of the flowi for
that dst. Unfortunately, the code that allocates and fills this copy
doesn't care about what type of flowi (flowi, flowi4, flowi6) gets
passed. In multiple code paths (from raw_sendmsg, from TCP when
replying to a FIN, in vxlan, geneve, and gre), the flowi that gets
passed to xfrm is actually an on-stack flowi4, so we end up reading
stuff from the stack past the end of the flowi4 struct.

Since xfrm_dst->origin isn't used anywhere following commit
ca116922afa8 ("xfrm: Eliminate "fl" and "pol" args to
xfrm_bundle_ok()."), just get rid of it.  xfrm_dst->partner isn't used
either, so get rid of that too.

Fixes: 9d6ec938019c ("ipv4: Use flowi4 in public route lookup interfaces.")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
---
v2: change Fixes tag to the commit that actually introduced the issue

 include/net/xfrm.h     | 10 ----------
 net/xfrm/xfrm_policy.c | 47 -----------------------------------------------
 2 files changed, 57 deletions(-)

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 6793a30c66b1..7e7e2b0d2915 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -979,10 +979,6 @@ struct xfrm_dst {
 	struct flow_cache_object flo;
 	struct xfrm_policy *pols[XFRM_POLICY_TYPE_MAX];
 	int num_pols, num_xfrms;
-#ifdef CONFIG_XFRM_SUB_POLICY
-	struct flowi *origin;
-	struct xfrm_selector *partner;
-#endif
 	u32 xfrm_genid;
 	u32 policy_genid;
 	u32 route_mtu_cached;
@@ -998,12 +994,6 @@ static inline void xfrm_dst_destroy(struct xfrm_dst *xdst)
 	dst_release(xdst->route);
 	if (likely(xdst->u.dst.xfrm))
 		xfrm_state_put(xdst->u.dst.xfrm);
-#ifdef CONFIG_XFRM_SUB_POLICY
-	kfree(xdst->origin);
-	xdst->origin = NULL;
-	kfree(xdst->partner);
-	xdst->partner = NULL;
-#endif
 }
 #endif
 
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index b00a1d5a7f52..ed4e52d95172 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -1797,43 +1797,6 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy,
 	goto out;
 }
 
-#ifdef CONFIG_XFRM_SUB_POLICY
-static int xfrm_dst_alloc_copy(void **target, const void *src, int size)
-{
-	if (!*target) {
-		*target = kmalloc(size, GFP_ATOMIC);
-		if (!*target)
-			return -ENOMEM;
-	}
-
-	memcpy(*target, src, size);
-	return 0;
-}
-#endif
-
-static int xfrm_dst_update_parent(struct dst_entry *dst,
-				  const struct xfrm_selector *sel)
-{
-#ifdef CONFIG_XFRM_SUB_POLICY
-	struct xfrm_dst *xdst = (struct xfrm_dst *)dst;
-	return xfrm_dst_alloc_copy((void **)&(xdst->partner),
-				   sel, sizeof(*sel));
-#else
-	return 0;
-#endif
-}
-
-static int xfrm_dst_update_origin(struct dst_entry *dst,
-				  const struct flowi *fl)
-{
-#ifdef CONFIG_XFRM_SUB_POLICY
-	struct xfrm_dst *xdst = (struct xfrm_dst *)dst;
-	return xfrm_dst_alloc_copy((void **)&(xdst->origin), fl, sizeof(*fl));
-#else
-	return 0;
-#endif
-}
-
 static int xfrm_expand_policies(const struct flowi *fl, u16 family,
 				struct xfrm_policy **pols,
 				int *num_pols, int *num_xfrms)
@@ -1905,16 +1868,6 @@ xfrm_resolve_and_create_bundle(struct xfrm_policy **pols, int num_pols,
 
 	xdst = (struct xfrm_dst *)dst;
 	xdst->num_xfrms = err;
-	if (num_pols > 1)
-		err = xfrm_dst_update_parent(dst, &pols[1]->selector);
-	else
-		err = xfrm_dst_update_origin(dst, fl);
-	if (unlikely(err)) {
-		dst_free(dst);
-		XFRM_INC_STATS(net, LINUX_MIB_XFRMOUTBUNDLECHECKERROR);
-		return ERR_PTR(err);
-	}
-
 	xdst->num_pols = num_pols;
 	memcpy(xdst->pols, pols, sizeof(struct xfrm_policy *) * num_pols);
 	xdst->policy_genid = atomic_read(&pols[0]->genid);
-- 
2.12.2

Re: [PATCH v2 net] xfrm: fix stack access out of bounds with CONFIG_XFRM_SUB_POLICY

[Steffen Klassert]

On Wed, May 03, 2017 at 04:43:19PM +0200, Sabrina Dubroca wrote:
> When CONFIG_XFRM_SUB_POLICY=y, xfrm_dst stores a copy of the flowi for
> that dst. Unfortunately, the code that allocates and fills this copy
> doesn't care about what type of flowi (flowi, flowi4, flowi6) gets
> passed. In multiple code paths (from raw_sendmsg, from TCP when
> replying to a FIN, in vxlan, geneve, and gre), the flowi that gets
> passed to xfrm is actually an on-stack flowi4, so we end up reading
> stuff from the stack past the end of the flowi4 struct.
> 
> Since xfrm_dst->origin isn't used anywhere following commit
> ca116922afa8 ("xfrm: Eliminate "fl" and "pol" args to
> xfrm_bundle_ok()."), just get rid of it.  xfrm_dst->partner isn't used
> either, so get rid of that too.
> 
> Fixes: 9d6ec938019c ("ipv4: Use flowi4 in public route lookup interfaces.")
> Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>

Applied to the ipsec tree, thanks Sabrina!