netdev - Re: BUG triggered in tcp_openreq_init_rwin most likely due to 13d3b1ebe2876

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Date:   Mon, 17 Jul 2017 08:18:54 +0000
From:   Lawrence Brakmo <brakmo@...com>
To:     David Ahern <dsahern@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: BUG triggered in tcp_openreq_init_rwin most likely due to
 13d3b1ebe2876

David, thank you for bringing this up. Sorry for the delay but I had been traveling. I will look into it.

- Lawrence

On 7/16/17, 4:47 PM, "David Ahern" <dsahern@...il.com> wrote:

    Hi:
    
    I am getting the following while testing IPv6 changes:
    
    [ 3904.250981] TCP: request_sock_TCPv6: Possible SYN flooding on port
    12345. Sending cookies.  Check SNMP counters.
    [ 3904.252862]
    ==================================================================
    [ 3904.254057] BUG: KASAN: null-ptr-deref in
    tcp_openreq_init_rwin+0x1d5/0x2b4
    [ 3904.255113] Read of size 1 at addr 0000000000000012 by task vrf-test/1166
    [ 3904.256149]
    [ 3904.256405] CPU: 0 PID: 1166 Comm: vrf-test Not tainted 4.12.0+ #307
    [ 3904.257373] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
    BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
    [ 3904.258899] Call Trace:
    [ 3904.259291]  <IRQ>
    [ 3904.259629]  dump_stack+0x81/0xb6
    [ 3904.260167]  kasan_report+0x234/0x269
    [ 3904.260688]  __asan_load1+0x45/0x47
    [ 3904.261176]  tcp_openreq_init_rwin+0x1d5/0x2b4
    [ 3904.261811]  tcp_conn_request+0xb1e/0xe11
    [ 3904.262448]  tcp_v6_conn_request+0x72/0x85
    [ 3904.263010]  ? tcp_v6_conn_request+0x72/0x85
    [ 3904.263605]  tcp_rcv_state_process+0xe6/0x1243
    [ 3904.264236]  ? lock_release+0x27f/0x444
    [ 3904.264793]  tcp_v6_do_rcv+0x321/0x559
    [ 3904.265316]  ? tcp_v6_do_rcv+0x321/0x559
    [ 3904.265858]  ? tcp_filter+0x82/0x95
    [ 3904.266357]  tcp_v6_rcv+0x6c7/0xb33
    [ 3904.266886]  ip6_input_finish+0x1de/0x5ca
    [ 3904.267471]  ip6_input+0x66/0x6c
    
    
    This is enough to prevent the problem the crash which suggest the recent
    bpf sock_ops is the culprit:
    
    diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
    index 0ff83c1637d8..88904882b4ad 100644
    --- a/net/ipv4/tcp_minisocks.c
    +++ b/net/ipv4/tcp_minisocks.c
    @@ -364,7 +364,7 @@ void tcp_openreq_init_rwin(struct request_sock *req,
                (req->rsk_window_clamp > full_space || req->rsk_window_clamp
    == 0))
                    req->rsk_window_clamp = full_space;
    
    -       rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req);
    +       rcv_wnd = 0; // tcp_rwnd_init_bpf((struct sock *)req);
            if (rcv_wnd == 0)
                    rcv_wnd = dst_metric(dst, RTAX_INITRWND);
            else if (full_space < rcv_wnd * mss)
    
    
    Note: I am *not* using any of the new sock_ops hooks; I simply have the
    cgroup bpf hooks enabled and in use for VRF.
    
    Reproduction includes creating a VRF and enabling cgroup code for it:
        ip li add red type vrf table 123
        ip li set red up
        ip addr add dev red 172.16.1.1/32
        ip vrf exec red ping -c1 172.16.1.1
    
    By adding vrf bpf to a cgroup the cgroup_bpf_enabled is set causing the
    rest of BPF_CGROUP_RUN_PROG_SOCK_OPS to be evaluated.
    
    From here, use your favorite test server and make SYN-ACKs get lost (not
    sure that is required but is a reliable trigger for me). In my case I am
    using my a simple networking test program:
    
    ip6tables -A INPUT -p tcp --sport 12345 -j DROP
    vrf-test -6 -s &
    vrf-test -6 -r 2001:db8:1::1 &
    vrf-test -6 -r 2001:db8:1::1 &
    <BOOM>