fuse: check connected before queueing on fpq->io

A request could end up on the fpq->io list after fuse_abort_conn() has
reset fpq->connected and aborted requests on that list:

Thread-1			  Thread-2
========			  ========
->fuse_simple_request()           ->shutdown
  ->__fuse_request_send()
    ->queue_request()		->fuse_abort_conn()
->fuse_dev_do_read()                ->acquire(fpq->lock)
  ->wait_for(fpq->lock) 	  ->set err to all req's in fpq->io
				  ->release(fpq->lock)
  ->acquire(fpq->lock)
  ->add req to fpq->io

After the userspace copy is done the request will be ended, but
req->out.h.error will remain uninitialized.  Also the copy might block
despite being already aborted.

Fix both issues by not allowing the request to be queued on the fpq->io
list after fuse_abort_conn() has processed this list.

Reported-by: Pradeep P V K <pragalla@codeaurora.org>
Fixes: fd22d62ed0c3 ("fuse: no fc->lock for iqueue parts")
Cc: <stable@vger.kernel.org> # v4.2
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 817a0b1..6e63bcb 100644 (file)
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1272,6 +1272,15 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
                goto restart;
        }
        spin_lock(&fpq->lock);
+       /*
+        *  Must not put request on fpq->io queue after having been shut down by
+        *  fuse_abort_conn()
+        */
+       if (!fpq->connected) {
+               req->out.h.error = err = -ECONNABORTED;
+               goto out_end;
+
+       }
        list_add(&req->list, &fpq->io);
        spin_unlock(&fpq->lock);
        cs->req = req;