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    Subject[PATCH 4.9 051/240] openvswitch: fix stack OOB read while fragmenting IPv4 packets
    Date
    From: Davide Caratti <dcaratti@redhat.com>

    commit 7c0ea5930c1c211931819d83cfb157bff1539a4c upstream.

    running openvswitch on kernels built with KASAN, it's possible to see the
    following splat while testing fragmentation of IPv4 packets:

    BUG: KASAN: stack-out-of-bounds in ip_do_fragment+0x1b03/0x1f60
    Read of size 1 at addr ffff888112fc713c by task handler2/1367

    CPU: 0 PID: 1367 Comm: handler2 Not tainted 5.12.0-rc6+ #418
    Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014
    Call Trace:
    dump_stack+0x92/0xc1
    print_address_description.constprop.7+0x1a/0x150
    kasan_report.cold.13+0x7f/0x111
    ip_do_fragment+0x1b03/0x1f60
    ovs_fragment+0x5bf/0x840 [openvswitch]
    do_execute_actions+0x1bd5/0x2400 [openvswitch]
    ovs_execute_actions+0xc8/0x3d0 [openvswitch]
    ovs_packet_cmd_execute+0xa39/0x1150 [openvswitch]
    genl_family_rcv_msg_doit.isra.15+0x227/0x2d0
    genl_rcv_msg+0x287/0x490
    netlink_rcv_skb+0x120/0x380
    genl_rcv+0x24/0x40
    netlink_unicast+0x439/0x630
    netlink_sendmsg+0x719/0xbf0
    sock_sendmsg+0xe2/0x110
    ____sys_sendmsg+0x5ba/0x890
    ___sys_sendmsg+0xe9/0x160
    __sys_sendmsg+0xd3/0x170
    do_syscall_64+0x33/0x40
    entry_SYSCALL_64_after_hwframe+0x44/0xae
    RIP: 0033:0x7f957079db07
    Code: c3 66 90 41 54 41 89 d4 55 48 89 f5 53 89 fb 48 83 ec 10 e8 eb ec ff ff 44 89 e2 48 89 ee 89 df 41 89 c0 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 48 89 44 24 08 e8 24 ed ff ff 48
    RSP: 002b:00007f956ce35a50 EFLAGS: 00000293 ORIG_RAX: 000000000000002e
    RAX: ffffffffffffffda RBX: 0000000000000019 RCX: 00007f957079db07
    RDX: 0000000000000000 RSI: 00007f956ce35ae0 RDI: 0000000000000019
    RBP: 00007f956ce35ae0 R08: 0000000000000000 R09: 00007f9558006730
    R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
    R13: 00007f956ce37308 R14: 00007f956ce35f80 R15: 00007f956ce35ae0

    The buggy address belongs to the page:
    page:00000000af2a1d93 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x112fc7
    flags: 0x17ffffc0000000()
    raw: 0017ffffc0000000 0000000000000000 dead000000000122 0000000000000000
    raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
    page dumped because: kasan: bad access detected

    addr ffff888112fc713c is located in stack of task handler2/1367 at offset 180 in frame:
    ovs_fragment+0x0/0x840 [openvswitch]

    this frame has 2 objects:
    [32, 144) 'ovs_dst'
    [192, 424) 'ovs_rt'

    Memory state around the buggy address:
    ffff888112fc7000: f3 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    ffff888112fc7080: 00 f1 f1 f1 f1 00 00 00 00 00 00 00 00 00 00 00
    >ffff888112fc7100: 00 00 00 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00
    ^
    ffff888112fc7180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    ffff888112fc7200: 00 00 00 00 00 00 f2 f2 f2 00 00 00 00 00 00 00

    for IPv4 packets, ovs_fragment() uses a temporary struct dst_entry. Then,
    in the following call graph:

    ip_do_fragment()
    ip_skb_dst_mtu()
    ip_dst_mtu_maybe_forward()
    ip_mtu_locked()

    the pointer to struct dst_entry is used as pointer to struct rtable: this
    turns the access to struct members like rt_mtu_locked into an OOB read in
    the stack. Fix this changing the temporary variable used for IPv4 packets
    in ovs_fragment(), similarly to what is done for IPv6 few lines below.

    Fixes: d52e5a7e7ca4 ("ipv4: lock mtu in fnhe when received PMTU < net.ipv4.route.min_pmt")
    Cc: <stable@vger.kernel.org>
    Acked-by: Eelco Chaudron <echaudro@redhat.com>
    Signed-off-by: Davide Caratti <dcaratti@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/openvswitch/actions.c | 8 ++++----
    1 file changed, 4 insertions(+), 4 deletions(-)

    --- a/net/openvswitch/actions.c
    +++ b/net/openvswitch/actions.c
    @@ -710,16 +710,16 @@ static void ovs_fragment(struct net *net
    }

    if (ethertype == htons(ETH_P_IP)) {
    - struct dst_entry ovs_dst;
    + struct rtable ovs_rt = { 0 };
    unsigned long orig_dst;

    prepare_frag(vport, skb);
    - dst_init(&ovs_dst, &ovs_dst_ops, NULL, 1,
    + dst_init(&ovs_rt.dst, &ovs_dst_ops, NULL, 1,
    DST_OBSOLETE_NONE, DST_NOCOUNT);
    - ovs_dst.dev = vport->dev;
    + ovs_rt.dst.dev = vport->dev;

    orig_dst = skb->_skb_refdst;
    - skb_dst_set_noref(skb, &ovs_dst);
    + skb_dst_set_noref(skb, &ovs_rt.dst);
    IPCB(skb)->frag_max_size = mru;

    ip_do_fragment(net, skb->sk, skb, ovs_vport_output);

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