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    Subject[PATCH 5.10 144/167] io_uring: explicitly count entries for poll reqs
    Date
    From: Pavel Begunkov <asml.silence@gmail.com>

    commit 68b11e8b1562986c134764433af64e97d30c9fc0 upstream.

    If __io_queue_proc() fails to add a second poll entry, e.g. kmalloc()
    failed, but it goes on with a third waitqueue, it may succeed and
    overwrite the error status. Count the number of poll entries we added,
    so we can set pt->error to zero at the beginning and find out when the
    mentioned scenario happens.

    Cc: stable@vger.kernel.org
    Fixes: 18bceab101add ("io_uring: allow POLL_ADD with double poll_wait() users")
    Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
    Link: https://lore.kernel.org/r/9d6b9e561f88bcc0163623b74a76c39f712151c3.1626774457.git.asml.silence@gmail.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    fs/io_uring.c | 16 ++++++++++------
    1 file changed, 10 insertions(+), 6 deletions(-)

    --- a/fs/io_uring.c
    +++ b/fs/io_uring.c
    @@ -4916,6 +4916,7 @@ static int io_connect(struct io_kiocb *r
    struct io_poll_table {
    struct poll_table_struct pt;
    struct io_kiocb *req;
    + int nr_entries;
    int error;
    };

    @@ -5098,11 +5099,11 @@ static void __io_queue_proc(struct io_po
    struct io_kiocb *req = pt->req;

    /*
    - * If poll->head is already set, it's because the file being polled
    - * uses multiple waitqueues for poll handling (eg one for read, one
    - * for write). Setup a separate io_poll_iocb if this happens.
    + * The file being polled uses multiple waitqueues for poll handling
    + * (e.g. one for read, one for write). Setup a separate io_poll_iocb
    + * if this happens.
    */
    - if (unlikely(poll->head)) {
    + if (unlikely(pt->nr_entries)) {
    struct io_poll_iocb *poll_one = poll;

    /* already have a 2nd entry, fail a third attempt */
    @@ -5124,7 +5125,7 @@ static void __io_queue_proc(struct io_po
    *poll_ptr = poll;
    }

    - pt->error = 0;
    + pt->nr_entries++;
    poll->head = head;

    if (poll->events & EPOLLEXCLUSIVE)
    @@ -5210,9 +5211,12 @@ static __poll_t __io_arm_poll_handler(st

    ipt->pt._key = mask;
    ipt->req = req;
    - ipt->error = -EINVAL;
    + ipt->error = 0;
    + ipt->nr_entries = 0;

    mask = vfs_poll(req->file, &ipt->pt) & poll->events;
    + if (unlikely(!ipt->nr_entries) && !ipt->error)
    + ipt->error = -EINVAL;

    spin_lock_irq(&ctx->completion_lock);
    if (likely(poll->head)) {

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