netdev - Re: [PATCH net] tcp: md5: reject TCP_MD5SIG or TCP_MD5SIG

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Date:   Thu, 12 Apr 2018 09:02:33 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net] tcp: md5: reject TCP_MD5SIG or TCP_MD5SIG_EXT on
 established sockets

On Wed, Apr 11, 2018 at 2:36 PM, Eric Dumazet <edumazet@...gle.com> wrote:
>
> syzbot/KMSAN reported an uninit-value in tcp_parse_options() [1]
>
> I believe this was caused by a TCP_MD5SIG being set on live
> flow.
>
> This is highly unexpected, since TCP option space is limited.
>
> For instance, presence of TCP MD5 option automatically disables
> TCP TimeStamp option at SYN/SYNACK time, which we can not do
> once flow has been established.
>
> Really, adding/deleting an MD5 key only makes sense on sockets
> in CLOSE or LISTEN state.
>
> [1]
> BUG: KMSAN: uninit-value in tcp_parse_options+0xd74/0x1a30 net/ipv4/tcp_input.c:3720
> CPU: 1 PID: 6177 Comm: syzkaller192004 Not tainted 4.16.0+ #83
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:17 [inline]
>  dump_stack+0x185/0x1d0 lib/dump_stack.c:53
>  kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
>  __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:676
>  tcp_parse_options+0xd74/0x1a30 net/ipv4/tcp_input.c:3720
>  tcp_fast_parse_options net/ipv4/tcp_input.c:3858 [inline]
>  tcp_validate_incoming+0x4f1/0x2790 net/ipv4/tcp_input.c:5184
>  tcp_rcv_established+0xf60/0x2bb0 net/ipv4/tcp_input.c:5453
>  tcp_v4_do_rcv+0x6cd/0xd90 net/ipv4/tcp_ipv4.c:1469
>  sk_backlog_rcv include/net/sock.h:908 [inline]
>  __release_sock+0x2d6/0x680 net/core/sock.c:2271
>  release_sock+0x97/0x2a0 net/core/sock.c:2786
>  tcp_sendmsg+0xd6/0x100 net/ipv4/tcp.c:1464
>  inet_sendmsg+0x48d/0x740 net/ipv4/af_inet.c:764
>  sock_sendmsg_nosec net/socket.c:630 [inline]
>  sock_sendmsg net/socket.c:640 [inline]
>  SYSC_sendto+0x6c3/0x7e0 net/socket.c:1747
>  SyS_sendto+0x8a/0xb0 net/socket.c:1715
>  do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
> RIP: 0033:0x448fe9
> RSP: 002b:00007fd472c64d38 EFLAGS: 00000216 ORIG_RAX: 000000000000002c
> RAX: ffffffffffffffda RBX: 00000000006e5a30 RCX: 0000000000448fe9
> RDX: 000000000000029f RSI: 0000000020a88f88 RDI: 0000000000000004
> RBP: 00000000006e5a34 R08: 0000000020e68000 R09: 0000000000000010
> R10: 00000000200007fd R11: 0000000000000216 R12: 0000000000000000
> R13: 00007fff074899ef R14: 00007fd472c659c0 R15: 0000000000000009
>
> Uninit was created at:
>  kmsan_save_stack_with_flags mm/kmsan/kmsan.c:278 [inline]
>  kmsan_internal_poison_shadow+0xb8/0x1b0 mm/kmsan/kmsan.c:188
>  kmsan_kmalloc+0x94/0x100 mm/kmsan/kmsan.c:314
>  kmsan_slab_alloc+0x11/0x20 mm/kmsan/kmsan.c:321
>  slab_post_alloc_hook mm/slab.h:445 [inline]
>  slab_alloc_node mm/slub.c:2737 [inline]
>  __kmalloc_node_track_caller+0xaed/0x11c0 mm/slub.c:4369
>  __kmalloc_reserve net/core/skbuff.c:138 [inline]
>  __alloc_skb+0x2cf/0x9f0 net/core/skbuff.c:206
>  alloc_skb include/linux/skbuff.h:984 [inline]
>  tcp_send_ack+0x18c/0x910 net/ipv4/tcp_output.c:3624
>  __tcp_ack_snd_check net/ipv4/tcp_input.c:5040 [inline]
>  tcp_ack_snd_check net/ipv4/tcp_input.c:5053 [inline]
>  tcp_rcv_established+0x2103/0x2bb0 net/ipv4/tcp_input.c:5469
>  tcp_v4_do_rcv+0x6cd/0xd90 net/ipv4/tcp_ipv4.c:1469
>  sk_backlog_rcv include/net/sock.h:908 [inline]
>  __release_sock+0x2d6/0x680 net/core/sock.c:2271
>  release_sock+0x97/0x2a0 net/core/sock.c:2786
>  tcp_sendmsg+0xd6/0x100 net/ipv4/tcp.c:1464
>  inet_sendmsg+0x48d/0x740 net/ipv4/af_inet.c:764
>  sock_sendmsg_nosec net/socket.c:630 [inline]
>  sock_sendmsg net/socket.c:640 [inline]
>  SYSC_sendto+0x6c3/0x7e0 net/socket.c:1747
>  SyS_sendto+0x8a/0xb0 net/socket.c:1715
>  do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
>
> Fixes: cfb6eeb4c860 ("[TCP]: MD5 Signature Option (RFC2385) support.")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> ---
Acked-by: Yuchung Cheng <ycheng@...gle.com>

Thanks for the fix!
>  net/ipv4/tcp.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index bccc4c2700870b8c7ff592a6bd27acebd9bc6471..4fa3f812b9ff8954a9b6a018c648ff12ab995721 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2813,8 +2813,10 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
>  #ifdef CONFIG_TCP_MD5SIG
>         case TCP_MD5SIG:
>         case TCP_MD5SIG_EXT:
> -               /* Read the IP->Key mappings from userspace */
> -               err = tp->af_specific->md5_parse(sk, optname, optval, optlen);
> +               if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
> +                       err = tp->af_specific->md5_parse(sk, optname, optval, optlen);
> +               else
> +                       err = -EINVAL;
>                 break;
>  #endif
>         case TCP_USER_TIMEOUT:
> --
> 2.17.0.484.g0c8726318c-goog
>