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    Subject[PATCH 4.15 35/72] netfilter: drop template ct when conntrack is skipped.
    Date
    4.15-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Paolo Abeni <pabeni@redhat.com>

    commit aebfa52a925d701114afd6af0def35bab16d4f47 upstream.

    The ipv4 nf_ct code currently skips the nf_conntrak_in() call
    for fragmented packets. As a results later matches/target can end
    up manipulating template ct entry instead of 'real' ones.

    Exploiting the above, syzbot found a way to trigger the following
    splat:

    WARNING: CPU: 1 PID: 4242 at net/netfilter/xt_cluster.c:55
    xt_cluster_mt+0x6c1/0x840 net/netfilter/xt_cluster.c:127
    Kernel panic - not syncing: panic_on_warn set ...

    CPU: 1 PID: 4242 Comm: syzkaller027971 Not tainted 4.16.0-rc2+ #243
    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+0x194/0x24d lib/dump_stack.c:53
    panic+0x1e4/0x41c kernel/panic.c:183
    __warn+0x1dc/0x200 kernel/panic.c:547
    report_bug+0x211/0x2d0 lib/bug.c:184
    fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
    fixup_bug arch/x86/kernel/traps.c:247 [inline]
    do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
    do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
    invalid_op+0x58/0x80 arch/x86/entry/entry_64.S:957
    RIP: 0010:xt_cluster_hash net/netfilter/xt_cluster.c:55 [inline]
    RIP: 0010:xt_cluster_mt+0x6c1/0x840 net/netfilter/xt_cluster.c:127
    RSP: 0018:ffff8801d2f6f2d0 EFLAGS: 00010293
    RAX: ffff8801af700540 RBX: 0000000000000000 RCX: ffffffff84a2d1e1
    RDX: 0000000000000000 RSI: ffff8801d2f6f478 RDI: ffff8801cafd336a
    RBP: ffff8801d2f6f2e8 R08: 0000000000000000 R09: 0000000000000001
    R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801b03b3d18
    R13: ffff8801cafd3300 R14: dffffc0000000000 R15: ffff8801d2f6f478
    ipt_do_table+0xa91/0x19b0 net/ipv4/netfilter/ip_tables.c:296
    iptable_filter_hook+0x65/0x80 net/ipv4/netfilter/iptable_filter.c:41
    nf_hook_entry_hookfn include/linux/netfilter.h:120 [inline]
    nf_hook_slow+0xba/0x1a0 net/netfilter/core.c:483
    nf_hook include/linux/netfilter.h:243 [inline]
    NF_HOOK include/linux/netfilter.h:286 [inline]
    raw_send_hdrinc.isra.17+0xf39/0x1880 net/ipv4/raw.c:432
    raw_sendmsg+0x14cd/0x26b0 net/ipv4/raw.c:669
    inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
    sock_sendmsg_nosec net/socket.c:629 [inline]
    sock_sendmsg+0xca/0x110 net/socket.c:639
    SYSC_sendto+0x361/0x5c0 net/socket.c:1748
    SyS_sendto+0x40/0x50 net/socket.c:1716
    do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287
    entry_SYSCALL_64_after_hwframe+0x42/0xb7
    RIP: 0033:0x441b49
    RSP: 002b:00007ffff5ca8b18 EFLAGS: 00000216 ORIG_RAX: 000000000000002c
    RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000441b49
    RDX: 0000000000000030 RSI: 0000000020ff7000 RDI: 0000000000000003
    RBP: 00000000006cc018 R08: 000000002066354c R09: 0000000000000010
    R10: 0000000000000000 R11: 0000000000000216 R12: 0000000000403470
    R13: 0000000000403500 R14: 0000000000000000 R15: 0000000000000000
    Dumping ftrace buffer:
    (ftrace buffer empty)
    Kernel Offset: disabled
    Rebooting in 86400 seconds..

    Instead of adding checks for template ct on every target/match
    manipulating skb->_nfct, simply drop the template ct when skipping
    nf_conntrack_in().

    Fixes: 7b4fdf77a450ec ("netfilter: don't track fragmented packets")
    Reported-and-tested-by: syzbot+0346441ae0545cfcea3a@syzkaller.appspotmail.com
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>
    Acked-by: Florian Westphal <fw@strlen.de>
    Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c | 14 +++++++++++++-
    1 file changed, 13 insertions(+), 1 deletion(-)

    --- a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
    +++ b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
    @@ -159,8 +159,20 @@ static unsigned int ipv4_conntrack_local
    ip_hdrlen(skb) < sizeof(struct iphdr))
    return NF_ACCEPT;

    - if (ip_is_fragment(ip_hdr(skb))) /* IP_NODEFRAG setsockopt set */
    + if (ip_is_fragment(ip_hdr(skb))) { /* IP_NODEFRAG setsockopt set */
    + enum ip_conntrack_info ctinfo;
    + struct nf_conn *tmpl;
    +
    + tmpl = nf_ct_get(skb, &ctinfo);
    + if (tmpl && nf_ct_is_template(tmpl)) {
    + /* when skipping ct, clear templates to avoid fooling
    + * later targets/matches
    + */
    + skb->_nfct = 0;
    + nf_ct_put(tmpl);
    + }
    return NF_ACCEPT;
    + }

    return nf_conntrack_in(state->net, PF_INET, state->hook, skb);
    }

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