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    Subject[PATCH 3.16 330/370] net: sctp, forbid negative length
    3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Jiri Slaby <jslaby@suse.cz>

    [ Upstream commit a4b8e71b05c27bae6bad3bdecddbc6b68a3ad8cf ]

    Most of getsockopt handlers in net/sctp/socket.c check len against
    sizeof some structure like:
    if (len < sizeof(int))
    return -EINVAL;

    On the first look, the check seems to be correct. But since len is int
    and sizeof returns size_t, int gets promoted to unsigned size_t too. So
    the test returns false for negative lengths. Yes, (-1 < sizeof(long)) is
    false.

    Fix this in sctp by explicitly checking len < 0 before any getsockopt
    handler is called.

    Note that sctp_getsockopt_events already handled the negative case.
    Since we added the < 0 check elsewhere, this one can be removed.

    If not checked, this is the result:
    UBSAN: Undefined behaviour in ../mm/page_alloc.c:2722:19
    shift exponent 52 is too large for 32-bit type 'int'
    CPU: 1 PID: 24535 Comm: syz-executor Not tainted 4.8.1-0-syzkaller #1
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
    0000000000000000 ffff88006d99f2a8 ffffffffb2f7bdea 0000000041b58ab3
    ffffffffb4363c14 ffffffffb2f7bcde ffff88006d99f2d0 ffff88006d99f270
    0000000000000000 0000000000000000 0000000000000034 ffffffffb5096422
    Call Trace:
    [<ffffffffb3051498>] ? __ubsan_handle_shift_out_of_bounds+0x29c/0x300
    ...
    [<ffffffffb273f0e4>] ? kmalloc_order+0x24/0x90
    [<ffffffffb27416a4>] ? kmalloc_order_trace+0x24/0x220
    [<ffffffffb2819a30>] ? __kmalloc+0x330/0x540
    [<ffffffffc18c25f4>] ? sctp_getsockopt_local_addrs+0x174/0xca0 [sctp]
    [<ffffffffc18d2bcd>] ? sctp_getsockopt+0x10d/0x1b0 [sctp]
    [<ffffffffb37c1219>] ? sock_common_getsockopt+0xb9/0x150
    [<ffffffffb37be2f5>] ? SyS_getsockopt+0x1a5/0x270

    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    Cc: Vlad Yasevich <vyasevich@gmail.com>
    Cc: Neil Horman <nhorman@tuxdriver.com>
    Cc: "David S. Miller" <davem@davemloft.net>
    Cc: linux-sctp@vger.kernel.org
    Cc: netdev@vger.kernel.org
    Acked-by: Neil Horman <nhorman@tuxdriver.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    net/sctp/socket.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    --- a/net/sctp/socket.c
    +++ b/net/sctp/socket.c
    @@ -4280,7 +4280,7 @@ static int sctp_getsockopt_disable_fragm
    static int sctp_getsockopt_events(struct sock *sk, int len, char __user *optval,
    int __user *optlen)
    {
    - if (len <= 0)
    + if (len == 0)
    return -EINVAL;
    if (len > sizeof(struct sctp_event_subscribe))
    len = sizeof(struct sctp_event_subscribe);
    @@ -5801,6 +5801,9 @@ static int sctp_getsockopt(struct sock *
    if (get_user(len, optlen))
    return -EFAULT;

    + if (len < 0)
    + return -EINVAL;
    +
    lock_sock(sk);

    switch (optname) {
    \
     
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