[PATCH 4.14 22/35] xfrm: refine validation of template and selector families

From: Greg Kroah-Hartman
Date: Wed Feb 13 2019 - 13:54:58 EST

4.14-stable review patch. If anyone has any objections, please let me know.


From: Florian Westphal <fw@xxxxxxxxx>

commit 35e6103861a3a970de6c84688c6e7a1f65b164ca upstream.

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_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@xxxxxxxxx
Reported-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

net/xfrm/xfrm_user.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -1445,10 +1445,15 @@ static int validate_tmpl(int nr, struct
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) {
+ break;
+ default:
+ if (ut[i].family != prev_family)
+ return -EINVAL;
+ break;
+ }
if (ut[i].mode >= XFRM_MODE_MAX)
return -EINVAL;