From mboxrd@z Thu Jan 1 00:00:00 1970 From: dsahern@kernel.org Subject: [PATCH net] net/ipv6: prevent use after free in ip6_route_mpath_notify Date: Mon, 4 Jun 2018 13:41:42 -0700 Message-ID: <20180604204142.8941-1-dsahern@kernel.org> Cc: David Ahern , Eric Dumazet To: netdev@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:48596 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751489AbeFDUlo (ORCPT ); Mon, 4 Jun 2018 16:41:44 -0400 Sender: netdev-owner@vger.kernel.org List-ID: From: David Ahern syzbot reported a use-after-free: BUG: KASAN: use-after-free in ip6_route_mpath_notify+0xe9/0x100 net/ipv6/route.c:4180 Read of size 4 at addr ffff8801bf789cf0 by task syz-executor756/4555 CPU: 1 PID: 4555 Comm: syz-executor756 Not tainted 4.17.0-rc7+ #78 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1b9/0x294 lib/dump_stack.c:113 print_address_description+0x6c/0x20b mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432 ip6_route_mpath_notify+0xe9/0x100 net/ipv6/route.c:4180 ip6_route_multipath_add+0x615/0x1910 net/ipv6/route.c:4303 inet6_rtm_newroute+0xe3/0x160 net/ipv6/route.c:4391 ... Allocated by task 4555: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490 kmem_cache_alloc+0x12e/0x760 mm/slab.c:3554 dst_alloc+0xbb/0x1d0 net/core/dst.c:104 __ip6_dst_alloc+0x35/0xa0 net/ipv6/route.c:361 ip6_dst_alloc+0x29/0xb0 net/ipv6/route.c:376 ip6_route_info_create+0x4d4/0x3a30 net/ipv6/route.c:2834 ip6_route_multipath_add+0xc7e/0x1910 net/ipv6/route.c:4240 inet6_rtm_newroute+0xe3/0x160 net/ipv6/route.c:4391 ... Freed by task 4555: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528 __cache_free mm/slab.c:3498 [inline] kmem_cache_free+0x86/0x2d0 mm/slab.c:3756 dst_destroy+0x267/0x3c0 net/core/dst.c:140 dst_release_immediate+0x71/0x9e net/core/dst.c:205 fib6_add+0xa40/0x1650 net/ipv6/ip6_fib.c:1305 __ip6_ins_rt+0x6c/0x90 net/ipv6/route.c:1011 ip6_route_multipath_add+0x513/0x1910 net/ipv6/route.c:4267 inet6_rtm_newroute+0xe3/0x160 net/ipv6/route.c:4391 ... The problem is that rt_last can point to a deleted route if the insert fails. One reproducer is to insert a route and then add a multipath route that has a duplicate nexthop.e.g,: $ ip -6 ro add vrf red 2001:db8:101::/64 nexthop via 2001:db8:1::2 $ ip -6 ro append vrf red 2001:db8:101::/64 nexthop via 2001:db8:1::4 nexthop via 2001:db8:1::2 Fix by not setting rt_last until the it is verified the insert succeeded. Fixes: 3b1137fe7482 ("net: ipv6: Change notifications for multipath add to RTA_MULTIPATH") Cc: Eric Dumazet Reported-by: syzbot Signed-off-by: David Ahern --- net/ipv6/route.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/net/ipv6/route.c b/net/ipv6/route.c index f4d61736c41a..c516f8556dbe 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -4263,11 +4263,15 @@ static int ip6_route_multipath_add(struct fib6_config *cfg, err_nh = NULL; list_for_each_entry(nh, &rt6_nh_list, next) { - rt_last = nh->rt6_info; err = __ip6_ins_rt(nh->rt6_info, info, &nh->mxc, extack); - /* save reference to first route for notification */ - if (!rt_notif && !err) - rt_notif = nh->rt6_info; + if (!err) { + /* save reference to last route successfully inserted */ + rt_last = nh->rt6_info; + + /* save reference to first route for notification */ + if (!rt_notif) + rt_notif = nh->rt6_info; + } /* nh->rt6_info is used or freed at this point, reset to NULL*/ nh->rt6_info = NULL; -- 2.11.0