KMSAN reported use of uninitialized memory in skb_set_hash_from_sk(),
which originated from the TCP request socket created in
cookie_v6_check():
==================================================================
BUG: KMSAN: use of uninitialized memory in tcp_transmit_skb+0xf77/0x3ec0
CPU: 1 PID: 2949 Comm: syz-execprog Not tainted 4.11.0-rc5+ #2931
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
TCP: request_sock_TCPv6: Possible SYN flooding on port 20028. Sending cookies. Check SNMP counters.
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:16
dump_stack+0x172/0x1c0 lib/dump_stack.c:52
kmsan_report+0x12a/0x180 mm/kmsan/kmsan.c:927
__msan_warning_32+0x61/0xb0 mm/kmsan/kmsan_instr.c:469
skb_set_hash_from_sk ./include/net/sock.h:2011
tcp_transmit_skb+0xf77/0x3ec0 net/ipv4/tcp_output.c:983
tcp_send_ack+0x75b/0x830 net/ipv4/tcp_output.c:3493
tcp_delack_timer_handler+0x9a6/0xb90 net/ipv4/tcp_timer.c:284
tcp_delack_timer+0x1b0/0x310 net/ipv4/tcp_timer.c:309
call_timer_fn+0x240/0x520 kernel/time/timer.c:1268
expire_timers kernel/time/timer.c:1307
__run_timers+0xc13/0xf10 kernel/time/timer.c:1601
run_timer_softirq+0x36/0xa0 kernel/time/timer.c:1614
__do_softirq+0x485/0x942 kernel/softirq.c:284
invoke_softirq kernel/softirq.c:364
irq_exit+0x1fa/0x230 kernel/softirq.c:405
exiting_irq+0xe/0x10 ./arch/x86/include/asm/apic.h:657
smp_apic_timer_interrupt+0x5a/0x80 arch/x86/kernel/apic/apic.c:966
apic_timer_interrupt+0x86/0x90 arch/x86/entry/entry_64.S:489
RIP: 0010:native_restore_fl ./arch/x86/include/asm/irqflags.h:36
RIP: 0010:arch_local_irq_restore ./arch/x86/include/asm/irqflags.h:77
RIP: 0010:__msan_poison_alloca+0xed/0x120 mm/kmsan/kmsan_instr.c:440
RSP: 0018:ffff880024917cd8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff10
RAX: 0000000000000246 RBX: ffff8800224c0000 RCX: 0000000000000005
RDX: 0000000000000004 RSI: ffff880000000000 RDI: ffffea0000b6d770
RBP: ffff880024917d58 R08: 0000000000000dd8 R09: 0000000000000004
R10: 0000160000000000 R11: 0000000000000000 R12: ffffffff85abf810
R13: ffff880024917dd8 R14: 0000000000000010 R15: ffffffff81cabde4
</IRQ>
poll_select_copy_remaining+0xac/0x6b0 fs/select.c:293
SYSC_select+0x4b4/0x4e0 fs/select.c:653
SyS_select+0x76/0xa0 fs/select.c:634
entry_SYSCALL_64_fastpath+0x13/0x94 arch/x86/entry/entry_64.S:204
RIP: 0033:0x4597e7
RSP: 002b:000000c420037ee0 EFLAGS: 00000246 ORIG_RAX: 0000000000000017
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004597e7
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 000000c420037ef0 R08: 000000c420037ee0 R09: 0000000000000059
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000042dc20
R13: 00000000000000f3 R14: 0000000000000030 R15: 0000000000000003
chained origin:
save_stack_trace+0x37/0x40 arch/x86/kernel/stacktrace.c:59
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:302
kmsan_save_stack mm/kmsan/kmsan.c:317
kmsan_internal_chain_origin+0x12a/0x1f0 mm/kmsan/kmsan.c:547
__msan_store_shadow_origin_4+0xac/0x110 mm/kmsan/kmsan_instr.c:259
tcp_create_openreq_child+0x709/0x1ae0 net/ipv4/tcp_minisocks.c:472
tcp_v6_syn_recv_sock+0x7eb/0x2a30 net/ipv6/tcp_ipv6.c:1103
tcp_get_cookie_sock+0x136/0x5f0 net/ipv4/syncookies.c:212
cookie_v6_check+0x17a9/0x1b50 net/ipv6/syncookies.c:245
tcp_v6_cookie_check net/ipv6/tcp_ipv6.c:989
tcp_v6_do_rcv+0xdd8/0x1c60 net/ipv6/tcp_ipv6.c:1298
tcp_v6_rcv+0x41a3/0x4f00 net/ipv6/tcp_ipv6.c:1487
ip6_input_finish+0x82f/0x1ee0 net/ipv6/ip6_input.c:279
NF_HOOK ./include/linux/netfilter.h:257
ip6_input+0x239/0x290 net/ipv6/ip6_input.c:322
dst_input ./include/net/dst.h:492
ip6_rcv_finish net/ipv6/ip6_input.c:69
NF_HOOK ./include/linux/netfilter.h:257
ipv6_rcv+0x1dbd/0x22e0 net/ipv6/ip6_input.c:203
__netif_receive_skb_core+0x2f6f/0x3a20 net/core/dev.c:4208
__netif_receive_skb net/core/dev.c:4246
process_backlog+0x667/0xba0 net/core/dev.c:4866
napi_poll net/core/dev.c:5268
net_rx_action+0xc95/0x1590 net/core/dev.c:5333
__do_softirq+0x485/0x942 kernel/softirq.c:284
origin:
save_stack_trace+0x37/0x40 arch/x86/kernel/stacktrace.c:59
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:302
kmsan_internal_poison_shadow+0xb1/0x1a0 mm/kmsan/kmsan.c:198
kmsan_kmalloc+0x7f/0xe0 mm/kmsan/kmsan.c:337
kmem_cache_alloc+0x1c2/0x1e0 mm/slub.c:2766
reqsk_alloc ./include/net/request_sock.h:87
inet_reqsk_alloc+0xa4/0x5b0 net/ipv4/tcp_input.c:6200
cookie_v6_check+0x4f4/0x1b50 net/ipv6/syncookies.c:169
tcp_v6_cookie_check net/ipv6/tcp_ipv6.c:989
tcp_v6_do_rcv+0xdd8/0x1c60 net/ipv6/tcp_ipv6.c:1298
tcp_v6_rcv+0x41a3/0x4f00 net/ipv6/tcp_ipv6.c:1487
ip6_input_finish+0x82f/0x1ee0 net/ipv6/ip6_input.c:279
NF_HOOK ./include/linux/netfilter.h:257
ip6_input+0x239/0x290 net/ipv6/ip6_input.c:322
dst_input ./include/net/dst.h:492
ip6_rcv_finish net/ipv6/ip6_input.c:69
NF_HOOK ./include/linux/netfilter.h:257
ipv6_rcv+0x1dbd/0x22e0 net/ipv6/ip6_input.c:203
__netif_receive_skb_core+0x2f6f/0x3a20 net/core/dev.c:4208
__netif_receive_skb net/core/dev.c:4246
process_backlog+0x667/0xba0 net/core/dev.c:4866
napi_poll net/core/dev.c:5268
net_rx_action+0xc95/0x1590 net/core/dev.c:5333
__do_softirq+0x485/0x942 kernel/softirq.c:284
==================================================================
Signed-off-by: Alexander Potapenko <[email protected]>
---
net/ipv6/syncookies.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 7b75b0620730..b4b354502c6e 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -216,6 +216,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
treq->rcv_isn = ntohl(th->seq) - 1;
treq->snt_isn = cookie;
treq->ts_off = 0;
+ treq->txhash = 0;
/*
* We need to lookup the dst_entry to get the correct window size.
--
2.13.2.932.g7449e964c-goog
On Fri, Jul 14, 2017 at 12:54 PM, Alexander Potapenko <[email protected]> wrote:
> KMSAN reported use of uninitialized memory in skb_set_hash_from_sk(),
> which originated from the TCP request socket created in
> cookie_v6_check():
...
> --- a/net/ipv6/syncookies.c
> +++ b/net/ipv6/syncookies.c
> @@ -216,6 +216,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
> treq->rcv_isn = ntohl(th->seq) - 1;
> treq->snt_isn = cookie;
> treq->ts_off = 0;
> + treq->txhash = 0;
>
> /*
> * We need to lookup the dst_entry to get the correct window size.
I would have thought that the same fix is needed in the corresponding
line in cookie_v4_check() in net/ipv4/syncookies.c? (I do not see
txhash being initialized for the IPv4 side.) If it's not needed for
some reason, then it would be worth a comment in the commit
description to explain why not.
thanks,
neal
On Fri, Jul 14, 2017 at 7:04 PM, Neal Cardwell <[email protected]> wrote:
> On Fri, Jul 14, 2017 at 12:54 PM, Alexander Potapenko <[email protected]> wrote:
>> KMSAN reported use of uninitialized memory in skb_set_hash_from_sk(),
>> which originated from the TCP request socket created in
>> cookie_v6_check():
> ...
>> --- a/net/ipv6/syncookies.c
>> +++ b/net/ipv6/syncookies.c
>> @@ -216,6 +216,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
>> treq->rcv_isn = ntohl(th->seq) - 1;
>> treq->snt_isn = cookie;
>> treq->ts_off = 0;
>> + treq->txhash = 0;
>>
>> /*
>> * We need to lookup the dst_entry to get the correct window size.
>
> I would have thought that the same fix is needed in the corresponding
> line in cookie_v4_check() in net/ipv4/syncookies.c? (I do not see
> txhash being initialized for the IPv4 side.) If it's not needed for
> some reason, then it would be worth a comment in the commit
> description to explain why not.
Most certainly it is needed. I haven't seen reports for that in the
wild and couldn't forge a repro triggering the bug in IPv4, but I'll
give it another shot.
> thanks,
> neal
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
On Fri, Jul 14, 2017 at 1:35 PM, Alexander Potapenko <[email protected]> wrote:
> On Fri, Jul 14, 2017 at 7:04 PM, Neal Cardwell <[email protected]> wrote:
>> On Fri, Jul 14, 2017 at 12:54 PM, Alexander Potapenko <[email protected]> wrote:
>>> KMSAN reported use of uninitialized memory in skb_set_hash_from_sk(),
>>> which originated from the TCP request socket created in
>>> cookie_v6_check():
>> ...
>>> --- a/net/ipv6/syncookies.c
>>> +++ b/net/ipv6/syncookies.c
>>> @@ -216,6 +216,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
>>> treq->rcv_isn = ntohl(th->seq) - 1;
>>> treq->snt_isn = cookie;
>>> treq->ts_off = 0;
>>> + treq->txhash = 0;
>>>
>>> /*
>>> * We need to lookup the dst_entry to get the correct window size.
>>
>> I would have thought that the same fix is needed in the corresponding
>> line in cookie_v4_check() in net/ipv4/syncookies.c? (I do not see
>> txhash being initialized for the IPv4 side.) If it's not needed for
>> some reason, then it would be worth a comment in the commit
>> description to explain why not.
> Most certainly it is needed. I haven't seen reports for that in the
> wild and couldn't forge a repro triggering the bug in IPv4, but I'll
> give it another shot.
If you force syncookies to be used, with:
sysctl -q net.ipv4.tcp_syncookies=2
then every passive IPv4 TCP connection that is accepted by a TCP
server app should be using that uninitialized memory, I would think
(and thus should be liable to fire the KMSAN use of uninitialized
memory warning).
Does that work?
neal
On Fri, 2017-07-14 at 18:54 +0200, Alexander Potapenko wrote:
> KMSAN reported use of uninitialized memory in skb_set_hash_from_sk(),
> which originated from the TCP request socket created in
> cookie_v6_check():
> ==================================================================
>
> Signed-off-by: Alexander Potapenko <[email protected]>
> ---
> net/ipv6/syncookies.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
> index 7b75b0620730..b4b354502c6e 100644
> --- a/net/ipv6/syncookies.c
> +++ b/net/ipv6/syncookies.c
> @@ -216,6 +216,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
> treq->rcv_isn = ntohl(th->seq) - 1;
> treq->snt_isn = cookie;
> treq->ts_off = 0;
> + treq->txhash = 0;
>
> /*
> * We need to lookup the dst_entry to get the correct window size.
Please use net_tx_rndhash() instead of 0, thanks.
( And same fix is needed for IPv4, as Neal mentioned already )
On Mon, 2017-07-17 at 00:39 -0700, Eric Dumazet wrote:
> On Fri, 2017-07-14 at 18:54 +0200, Alexander Potapenko wrote:
> > KMSAN reported use of uninitialized memory in skb_set_hash_from_sk(),
> > which originated from the TCP request socket created in
> > cookie_v6_check():
>
> > ==================================================================
> >
> > Signed-off-by: Alexander Potapenko <[email protected]>
> > ---
> > net/ipv6/syncookies.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
> > index 7b75b0620730..b4b354502c6e 100644
> > --- a/net/ipv6/syncookies.c
> > +++ b/net/ipv6/syncookies.c
> > @@ -216,6 +216,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
> > treq->rcv_isn = ntohl(th->seq) - 1;
> > treq->snt_isn = cookie;
> > treq->ts_off = 0;
> > + treq->txhash = 0;
> >
> > /*
> > * We need to lookup the dst_entry to get the correct window size.
>
> Please use net_tx_rndhash() instead of 0, thanks.
>
> ( And same fix is needed for IPv4, as Neal mentioned already )
Also please add the following tag.
Fixes: 58d607d3e52f ("tcp: provide skb->hash to synack packets")
Thanks again !