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SubjectRe: [PATCH] net/9p/trans_fd.c: fix race by holding the lock
Tomas Bortoli wrote on Mon, Jul 23, 2018:
> 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.
>
> Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
> Reported-by: syzbot+735d926e9d1317c3310c@syzkaller.appspotmail.com

OK, taking this one.

> ---
> net/9p/trans_fd.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
> index 588bf88c3305..f9f96d50d96d 100644
> --- a/net/9p/trans_fd.c
> +++ b/net/9p/trans_fd.c
> @@ -197,15 +197,14 @@ static void p9_mux_poll_stop(struct p9_conn *m)
> 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;
> }
>
> @@ -217,7 +216,6 @@ static void p9_conn_cancel(struct p9_conn *m, int err)
> 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);
> @@ -226,6 +224,7 @@ static void p9_conn_cancel(struct p9_conn *m, int err)
> req->t_err = err;
> p9_client_cb(m->client, req, REQ_STATUS_ERROR);
> }
> + spin_unlock(&m->client->lock);
> }
>
> static __poll_t
> @@ -373,8 +372,9 @@ static void p9_read_work(struct work_struct *work)
> 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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