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    Subject[PATCH 4.4 006/131] futex: Ensure that futex address is aligned in handle_futex_death()
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Chen Jie <chenjie6@huawei.com>

    commit 5a07168d8d89b00fe1760120714378175b3ef992 upstream.

    The futex code requires that the user space addresses of futexes are 32bit
    aligned. sys_futex() checks this in futex_get_keys() but the robust list
    code has no alignment check in place.

    As a consequence the kernel crashes on architectures with strict alignment
    requirements in handle_futex_death() when trying to cmpxchg() on an
    unaligned futex address which was retrieved from the robust list.

    [ tglx: Rewrote changelog, proper sizeof() based alignement check and add
    comment ]

    Fixes: 0771dfefc9e5 ("[PATCH] lightweight robust futexes: core")
    Signed-off-by: Chen Jie <chenjie6@huawei.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: <dvhart@infradead.org>
    Cc: <peterz@infradead.org>
    Cc: <zengweilin@huawei.com>
    Cc: stable@vger.kernel.org
    Link: https://lkml.kernel.org/r/1552621478-119787-1-git-send-email-chenjie6@huawei.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/futex.c | 4 ++++
    1 file changed, 4 insertions(+)

    --- a/kernel/futex.c
    +++ b/kernel/futex.c
    @@ -3067,6 +3067,10 @@ int handle_futex_death(u32 __user *uaddr
    {
    u32 uval, uninitialized_var(nval), mval;

    + /* Futex address must be 32bit aligned */
    + if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
    + return -1;
    +
    retry:
    if (get_user(uval, uaddr))
    return -1;

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