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    Subject[PATCH 3.18 25/93] l2tp: do not accept arbitrary sockets
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

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

    From: Eric Dumazet <edumazet@google.com>


    [ Upstream commit 17cfe79a65f98abe535261856c5aef14f306dff7 ]

    syzkaller found an issue caused by lack of sufficient checks
    in l2tp_tunnel_create()

    RAW sockets can not be considered as UDP ones for instance.

    In another patch, we shall replace all pr_err() by less intrusive
    pr_debug() so that syzkaller can find other bugs faster.
    Acked-by: Guillaume Nault <g.nault@alphalink.fr>
    Acked-by: James Chapman <jchapman@katalix.com>

    ==================================================================
    BUG: KASAN: slab-out-of-bounds in setup_udp_tunnel_sock+0x3ee/0x5f0 net/ipv4/udp_tunnel.c:69
    dst_release: dst:00000000d53d0d0f refcnt:-1
    Write of size 1 at addr ffff8801d013b798 by task syz-executor3/6242

    CPU: 1 PID: 6242 Comm: syz-executor3 Not tainted 4.16.0-rc2+ #253
    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
    print_address_description+0x73/0x250 mm/kasan/report.c:256
    kasan_report_error mm/kasan/report.c:354 [inline]
    kasan_report+0x23b/0x360 mm/kasan/report.c:412
    __asan_report_store1_noabort+0x17/0x20 mm/kasan/report.c:435
    setup_udp_tunnel_sock+0x3ee/0x5f0 net/ipv4/udp_tunnel.c:69
    l2tp_tunnel_create+0x1354/0x17f0 net/l2tp/l2tp_core.c:1596
    pppol2tp_connect+0x14b1/0x1dd0 net/l2tp/l2tp_ppp.c:707
    SYSC_connect+0x213/0x4a0 net/socket.c:1640
    SyS_connect+0x24/0x30 net/socket.c:1621
    do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287
    entry_SYSCALL_64_after_hwframe+0x42/0xb7

    Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/l2tp/l2tp_core.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    --- a/net/l2tp/l2tp_core.c
    +++ b/net/l2tp/l2tp_core.c
    @@ -1517,9 +1517,14 @@ int l2tp_tunnel_create(struct net *net,
    encap = cfg->encap;

    /* Quick sanity checks */
    + err = -EPROTONOSUPPORT;
    + if (sk->sk_type != SOCK_DGRAM) {
    + pr_debug("tunl %hu: fd %d wrong socket type\n",
    + tunnel_id, fd);
    + goto err;
    + }
    switch (encap) {
    case L2TP_ENCAPTYPE_UDP:
    - err = -EPROTONOSUPPORT;
    if (sk->sk_protocol != IPPROTO_UDP) {
    pr_err("tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
    tunnel_id, fd, sk->sk_protocol, IPPROTO_UDP);
    @@ -1527,7 +1532,6 @@ int l2tp_tunnel_create(struct net *net,
    }
    break;
    case L2TP_ENCAPTYPE_IP:
    - err = -EPROTONOSUPPORT;
    if (sk->sk_protocol != IPPROTO_L2TP) {
    pr_err("tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
    tunnel_id, fd, sk->sk_protocol, IPPROTO_L2TP);

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