[PATCH 3.16 298/328] ipv6: take rcu lock in rawv6_send_hdrinc()

Ben Hutchings
2018-12-09T21:55:58Z

From: Wei Wang <weiwan@google.com>

commit a688caa34beb2fd2a92f1b6d33e40cde433ba160 upstream.

In rawv6_send_hdrinc(), in order to avoid an extra dst_hold(), we
directly assign the dst to skb and set passed in dst to NULL to avoid
double free.
However, in error case, we free skb and then do stats update with the
dst pointer passed in. This causes use-after-free on the dst.
Fix it by taking rcu read lock right before dst could get released to
make sure dst does not get freed until the stats update is done.
Note: we don't have this issue in ipv4 cause dst is not used for stats
update in v4.

Syzkaller reported following crash:
BUG: KASAN: use-after-free in rawv6_send_hdrinc net/ipv6/raw.c:692 [inline]
BUG: KASAN: use-after-free in rawv6_sendmsg+0x4421/0x4630 net/ipv6/raw.c:921
Read of size 8 at addr ffff8801d95ba730 by task syz-executor0/32088

CPU: 1 PID: 32088 Comm: syz-executor0 Not tainted 4.19.0-rc2+ #93
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+0x1c4/0x2b4 lib/dump_stack.c:113
print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
rawv6_send_hdrinc net/ipv6/raw.c:692 [inline]
rawv6_sendmsg+0x4421/0x4630 net/ipv6/raw.c:921
inet_sendmsg+0x1a1/0x690 net/ipv4/af_inet.c:798
sock_sendmsg_nosec net/socket.c:621 [inline]
sock_sendmsg+0xd5/0x120 net/socket.c:631
___sys_sendmsg+0x7fd/0x930 net/socket.c:2114
__sys_sendmsg+0x11d/0x280 net/socket.c:2152
__do_sys_sendmsg net/socket.c:2161 [inline]
__se_sys_sendmsg net/socket.c:2159 [inline]
__x64_sys_sendmsg+0x78/0xb0 net/socket.c:2159
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457099
Code: fd b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 cb b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f83756edc78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f83756ee6d4 RCX: 0000000000457099
RDX: 0000000000000000 RSI: 0000000020003840 RDI: 0000000000000004
RBP: 00000000009300a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004d4b30 R14: 00000000004c90b1 R15: 0000000000000000

Allocated by task 32088:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
kmem_cache_alloc+0x12e/0x730 mm/slab.c:3554
dst_alloc+0xbb/0x1d0 net/core/dst.c:105
ip6_dst_alloc+0x35/0xa0 net/ipv6/route.c:353
ip6_rt_cache_alloc+0x247/0x7b0 net/ipv6/route.c:1186
ip6_pol_route+0x8f8/0xd90 net/ipv6/route.c:1895
ip6_pol_route_output+0x54/0x70 net/ipv6/route.c:2093
fib6_rule_lookup+0x277/0x860 net/ipv6/fib6_rules.c:122
ip6_route_output_flags+0x2c5/0x350 net/ipv6/route.c:2121
ip6_route_output include/net/ip6_route.h:88 [inline]
ip6_dst_lookup_tail+0xe27/0x1d60 net/ipv6/ip6_output.c:951
ip6_dst_lookup_flow+0xc8/0x270 net/ipv6/ip6_output.c:1079
rawv6_sendmsg+0x12d9/0x4630 net/ipv6/raw.c:905
inet_sendmsg+0x1a1/0x690 net/ipv4/af_inet.c:798
sock_sendmsg_nosec net/socket.c:621 [inline]
sock_sendmsg+0xd5/0x120 net/socket.c:631
___sys_sendmsg+0x7fd/0x930 net/socket.c:2114
__sys_sendmsg+0x11d/0x280 net/socket.c:2152
__do_sys_sendmsg net/socket.c:2161 [inline]
__se_sys_sendmsg net/socket.c:2159 [inline]
__x64_sys_sendmsg+0x78/0xb0 net/socket.c:2159
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 5356:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x102/0x150 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+0x83/0x290 mm/slab.c:3756
dst_destroy+0x267/0x3c0 net/core/dst.c:141
dst_destroy_rcu+0x16/0x19 net/core/dst.c:154
__rcu_reclaim kernel/rcu/rcu.h:236 [inline]
rcu_do_batch kernel/rcu/tree.c:2576 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:2880 [inline]
__rcu_process_callbacks kernel/rcu/tree.c:2847 [inline]
rcu_process_callbacks+0xf23/0x2670 kernel/rcu/tree.c:2864
__do_softirq+0x30b/0xad8 kernel/softirq.c:292

Fixes: 1789a640f556 ("raw: avoid two atomics in xmit")
Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16:
- We don't set tstamp here
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -643,8 +643,6 @@ static int rawv6_send_hdrinc(struct sock
skb->protocol = htons(ETH_P_IPV6);
skb->priority = sk->sk_priority;
skb->mark = sk->sk_mark;
- skb_dst_set(skb, &rt->dst);
- *dstp = NULL;

skb_put(skb, length);
skb_reset_network_header(skb);
@@ -654,24 +652,37 @@ static int rawv6_send_hdrinc(struct sock

skb->transport_header = skb->network_header;
err = memcpy_fromiovecend((void *)iph, from, 0, length);
- if (err)
- goto error_fault;
+ if (err) {
+ err = -EFAULT;
+ kfree_skb(skb);
+ goto error;
+ }

+ skb_dst_set(skb, &rt->dst);
+ *dstp = NULL;
+
+ /* Acquire rcu_read_lock() in case we need to use rt->rt6i_idev
+ * in the error path. Since skb has been freed, the dst could
+ * have been queued for deletion.
+ */
+ rcu_read_lock();
IP6_UPD_PO_STATS(net, rt->rt6i_idev, IPSTATS_MIB_OUT, skb->len);
err = NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT, skb, NULL,
rt->dst.dev, dst_output);
if (err > 0)
err = net_xmit_errno(err);
- if (err)
- goto error;
+ if (err) {
+ IP6_INC_STATS(net, rt->rt6i_idev, IPSTATS_MIB_OUTDISCARDS);
+ rcu_read_unlock();
+ goto error_check;
+ }
+ rcu_read_unlock();
out:
return 0;

-error_fault:
- err = -EFAULT;
- kfree_skb(skb);
error:
IP6_INC_STATS(net, rt->rt6i_idev, IPSTATS_MIB_OUTDISCARDS);
+error_check:
if (err == -ENOBUFS && !np->recverr)
err = 0;
return err;