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    SubjectRe: [RFC] unix: fix use-after-free in unix_dgram_poll()
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    On 10/28/2015 12:46 PM, Rainer Weikusat wrote:
    > Rainer Weikusat <rw@doppelsaurus.mobileactivedefense.com> writes:
    >> Jason Baron <jbaron@akamai.com> writes:
    >
    > [...]
    >
    >>> 2)
    >>>
    >>> For the case of epoll() in edge triggered mode we need to ensure that
    >>> when we return -EAGAIN from unix_dgram_sendmsg() when unix_recvq_full()
    >>> is true, we need to add a unix_peer_wake_connect() call to guarantee a
    >>> wakeup. Otherwise, we are going to potentially hang there.
    >>
    >> I consider this necessary.
    >
    > (As already discussed privately) just doing this would open up another
    > way for sockets to be enqueued on the peer_wait queue of the peer
    > forever despite no one wants to be notified of write space
    > availability. Here's another RFC patch addressing the issues so far plus
    > this one by breaking the connection to the peer socket from the wake up
    > relaying function. This has the nice additional property that the
    > dgram_poll code becomes somewhat simpler as the "dequeued where we
    > didn't enqueue" situation can no longer occur and the not-so-nice
    > additional property that the connect and disconnect functions need to
    > take the peer_wait.lock spinlock explicitly so that this lock is used to
    > ensure that no two threads modifiy the private pointer of the client
    > wait_queue_t.

    Hmmm...I thought these were already all guarded by unix_state_lock(sk).
    In any case, rest of the patch overall looks good to me.

    Thanks,

    -Jason



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