From: David Ahern <dsahern@xxxxxxxxx>
commit f7225172f25aaf0dfd9ad65f05be8da5d6108b12 upstream.
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.
Backport Note:
- Upstream has replaced rt6_info usage with fib6_info in 8d1c802b281
("net/ipv6: Flip FIB entries to fib6_info")
- fib6_info_release was introduced upstream in 93531c674315
("net/ipv6: separate handling of FIB entries from dst based routes"),
but is not present in stable kernels; 4.14.y relies on dst_release/
ip6_rt_put/dst_release_immediate.
Fixes: 3b1137fe7482 ("net: ipv6: Change notifications for multipath add to RTA_MULTIPATH")
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: David Ahern <dsahern@xxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Zubin Mithra <zsm@xxxxxxxxxxxx>
---
net/ipv6/route.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 60efd326014b..30204bc2fc48 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3239,11 +3239,16 @@ 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;
--
2.19.0.397.gdd90340f6a-goog
