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    Subject[PATCH 4.14 050/115] net/9p/trans_fd.c: fix race by holding the lock
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Tomas Bortoli <tomasbortoli@gmail.com>

    [ Upstream commit 9f476d7c540cb57556d3cc7e78704e6cd5100f5f ]

    It may be possible to run p9_fd_cancel() with a deleted req->req_list
    and incur in a double del. To fix hold the client->lock while changing
    the status, so the other threads will be synchronized.

    Link: http://lkml.kernel.org/r/20180723184253.6682-1-tomasbortoli@gmail.com
    Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
    Reported-by: syzbot+735d926e9d1317c3310c@syzkaller.appspotmail.com
    To: Eric Van Hensbergen <ericvh@gmail.com>
    To: Ron Minnich <rminnich@sandia.gov>
    To: Latchesar Ionkov <lucho@ionkov.net>
    Cc: Yiwen Jiang <jiangyiwen@huwei.com>
    Cc: David S. Miller <davem@davemloft.net>
    Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/9p/trans_fd.c | 10 +++++-----
    1 file changed, 5 insertions(+), 5 deletions(-)

    --- a/net/9p/trans_fd.c
    +++ b/net/9p/trans_fd.c
    @@ -199,15 +199,14 @@ static void p9_mux_poll_stop(struct p9_c
    static void p9_conn_cancel(struct p9_conn *m, int err)
    {
    struct p9_req_t *req, *rtmp;
    - unsigned long flags;
    LIST_HEAD(cancel_list);

    p9_debug(P9_DEBUG_ERROR, "mux %p err %d\n", m, err);

    - spin_lock_irqsave(&m->client->lock, flags);
    + spin_lock(&m->client->lock);

    if (m->err) {
    - spin_unlock_irqrestore(&m->client->lock, flags);
    + spin_unlock(&m->client->lock);
    return;
    }

    @@ -219,7 +218,6 @@ static void p9_conn_cancel(struct p9_con
    list_for_each_entry_safe(req, rtmp, &m->unsent_req_list, req_list) {
    list_move(&req->req_list, &cancel_list);
    }
    - spin_unlock_irqrestore(&m->client->lock, flags);

    list_for_each_entry_safe(req, rtmp, &cancel_list, req_list) {
    p9_debug(P9_DEBUG_ERROR, "call back req %p\n", req);
    @@ -228,6 +226,7 @@ static void p9_conn_cancel(struct p9_con
    req->t_err = err;
    p9_client_cb(m->client, req, REQ_STATUS_ERROR);
    }
    + spin_unlock(&m->client->lock);
    }

    static int
    @@ -385,8 +384,9 @@ static void p9_read_work(struct work_str
    if (m->req->status != REQ_STATUS_ERROR)
    status = REQ_STATUS_RCVD;
    list_del(&m->req->req_list);
    - spin_unlock(&m->client->lock);
    + /* update req->status while holding client->lock */
    p9_client_cb(m->client, m->req, status);
    + spin_unlock(&m->client->lock);
    m->rc.sdata = NULL;
    m->rc.offset = 0;
    m->rc.capacity = 0;

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