netdev - [PATCH ipsec] xfrm: refine validation of template and selector families

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Message-Id: <20190109133734.6482-1-fw@strlen.de>
Date:   Wed,  9 Jan 2019 14:37:34 +0100
From:   Florian Westphal <fw@...len.de>
To:     steffen.klassert@...unet.com
Cc:     3ntr0py1337@...il.com, daniel@...earbox.net,
        <netdev@...r.kernel.org>, Florian Westphal <fw@...len.de>
Subject: [PATCH ipsec] xfrm: refine validation of template and selector families

The check assumes that in transport mode, the first templates family
must match the address family of the policy selector.

Syzkaller managed to build a template using MODE_ROUTEOPTIMIZATION,
with ipv4-in-ipv6 chain, leading to following splat:

BUG: KASAN: stack-out-of-bounds in xfrm_state_find+0x1db/0x1854
Read of size 4 at addr ffff888063e57aa0 by task a.out/2050
 xfrm_state_find+0x1db/0x1854
 xfrm_tmpl_resolve+0x100/0x1d0
 xfrm_resolve_and_create_bundle+0x108/0x1000 [..]

Problem is that addresses point into flowi4 struct, but xfrm_state_find
treats them as being ipv6 because it uses templ->encap_family is used
(AF_INET6 in case of reproducer) rather than family (AF_INET).

This patch inverts the logic: Enforce 'template family must match
selector' EXCEPT for tunnel and BEET mode.

In BEET and Tunnel mode, xfrm_tmpl_resolve_one will have remote/local
address pointers changed to point at the addresses found in the template,
rather than the flowi ones, so no oob read will occur.

Reported-by: 3ntr0py1337@...il.com
Reported-by: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/xfrm/xfrm_user.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 277c1c46fe94..c6d26afcf89d 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -1488,10 +1488,15 @@ static int validate_tmpl(int nr, struct xfrm_user_tmpl *ut, u16 family)
 		if (!ut[i].family)
 			ut[i].family = family;

-		if ((ut[i].mode == XFRM_MODE_TRANSPORT) &&
-		    (ut[i].family != prev_family))
-			return -EINVAL;
-
+		switch (ut[i].mode) {
+		case XFRM_MODE_TUNNEL:
+		case XFRM_MODE_BEET:
+			break;
+		default:
+			if (ut[i].family != prev_family)
+				return -EINVAL;
+			break;
+		}
 		if (ut[i].mode >= XFRM_MODE_MAX)
 			return -EINVAL;

-- 
2.19.2