fuse: fix use-after-free in fuse_direct_IO()

commit ebacb81273599555a7a19f7754a1451206a5fc4f upstream.

In async IO blocking case the additional reference to the io is taken for
it to survive fuse_aio_complete(). In non blocking case this additional
reference is not needed, however we still reference io to figure out
whether to wait for completion or not. This is wrong and will lead to
use-after-free. Fix it by storing blocking information in separate
variable.

This was spotted by KASAN when running generic/208 fstest.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reported-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 744742d692e3 ("fuse: Add reference counting for fuse_io_priv")
Cc: <stable@vger.kernel.org> # v4.6
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 32d0b883e74f340d442754a5a87b82629b96658e..a0ffed34b85d23edb825756d424c00578124e182 100644 (file)
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2913,10 +2913,12 @@ fuse_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
        }
 
        if (io->async) {
+               bool blocking = io->blocking;
+
                fuse_aio_complete(io, ret < 0 ? ret : 0, -1);
 
                /* we have a non-extending, async request, so return */
-               if (!io->blocking)
+               if (!blocking)
                        return -EIOCBQUEUED;
 
                wait_for_completion(&wait);