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net/ipv6: prevent use after free in ip6_route_mpath_notify

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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: 3b1137fe74 ("net: ipv6: Change notifications for multipath add to RTA_MULTIPATH")
Cc: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David Ahern 2018-06-04 13:41:42 -07:00 committed by David S. Miller
parent 69e2ecccd0
commit f7225172f2
1 changed files with 8 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
net/ipv6/route.c
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@ -4412,13 +4412,17 @@ 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->fib6_info;
err = __ip6_ins_rt(nh->fib6_info, info, extack);
fib6_info_release(nh->fib6_info);
/* save reference to first route for notification */
if (!rt_notif && !err)
rt_notif = nh->fib6_info;
if (!err) {
/* save reference to last route successfully inserted */
rt_last = nh->fib6_info;
/* save reference to first route for notification */
if (!rt_notif)
rt_notif = nh->fib6_info;
}
/* nh->fib6_info is used or freed at this point, reset to NULL*/
nh->fib6_info = NULL;