Re: [PATCH] ipv4: ipv6: initialize treq->txhash in cookie_v[46]_check()

[Alexander Potapenko]

On Mon, Jul 17, 2017 at 12:35 PM, Alexander Potapenko <glider@xxxxxxxxxx> 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():
>
>  ==================================================================
>  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
>  ==================================================================
>
> Similar error is reported for cookie_v4_check().
>
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> Fixes: 58d607d3e52f ("tcp: provide skb->hash to synack packets")
> ---
What I forgot here is the patch changelog.
Per request from Eric Dumazet we initialize treq->txhash with the
result of net_tx_rndhash().
Per request from Neal Cardwell we do the same for IPv4.
>  net/ipv4/syncookies.c | 1 +
>  net/ipv6/syncookies.c | 1 +
>  2 files changed, 2 insertions(+)
>
> diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
> index 0905cf04c2a4..03ad8778c395 100644
> --- a/net/ipv4/syncookies.c
> +++ b/net/ipv4/syncookies.c
> @@ -335,6 +335,7 @@ struct sock *cookie_v4_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            = net_tx_rndhash();
>         req->mss                = mss;
>         ireq->ir_num            = ntohs(th->dest);
>         ireq->ir_rmt_port       = th->source;
> diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
> index 7b75b0620730..4e7817abc0b9 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 = net_tx_rndhash();
>
>         /*
>          * We need to lookup the dst_entry to get the correct window size.
> --
> 2.13.2.932.g7449e964c-goog
>



-- 
Alexander Potapenko
Software Engineer

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