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Tsirkin" To: Jason Wang Cc: Cong Zhang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , Paolo Bonzini , Stefan Hajnoczi , Jens Axboe , linux-arm-msm@vger.kernel.org, virtualization@lists.linux.dev, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, pavan.kondeti@oss.qualcomm.com Subject: Re: [PATCH] virtio_blk: NULL out vqs to avoid double free on failed resume Message-ID: <20251022030050-mutt-send-email-mst@kernel.org> References: <20251021-virtio_double_free-v1-1-4dd0cfd258f1@oss.qualcomm.com> <20251021085030-mutt-send-email-mst@kernel.org> <20251022014453-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20251022014453-mutt-send-email-mst@kernel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 43fU3TUoJsULXWEp998r2CG0gNKnDOHfgXylN9e3AXg_1761116469 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit On Wed, Oct 22, 2025 at 01:45:38AM -0400, Michael S. Tsirkin wrote: > On Wed, Oct 22, 2025 at 12:19:19PM +0800, Jason Wang wrote: > > On Tue, Oct 21, 2025 at 8:58 PM Michael S. Tsirkin wrote: > > > > > > On Tue, Oct 21, 2025 at 07:07:56PM +0800, Cong Zhang wrote: > > > > The vblk->vqs releases during freeze. If resume fails before vblk->vqs > > > > is allocated, later freeze/remove may attempt to free vqs again. > > > > Set vblk->vqs to NULL after freeing to avoid double free. > > > > > > > > Signed-off-by: Cong Zhang > > > > --- > > > > The patch fixes a double free issue that occurs in virtio_blk during > > > > freeze/resume. > > > > The issue is caused by: > > > > 1. During the first freeze, vblk->vqs is freed but pointer is not set to > > > > NULL. > > > > 2. Virtio block device fails before vblk->vqs is allocated during resume. > > > > 3. During the next freeze, vblk->vqs gets freed again, causing the > > > > double free crash. > > > > > > this part I don't get. if restore fails, how can freeze be called > > > again? > > > > For example, could it be triggered by the user? > > > > Thanks > > I don't know - were you able to trigger it? how? Sorry I mean the submitter of course. > > > > > > > > --- > > > > drivers/block/virtio_blk.c | 13 ++++++++++++- > > > > 1 file changed, 12 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > > > > index f061420dfb10c40b21765b173fab7046aa447506..746795066d7f56a01c9a9c0344d24f9fa06841eb 100644 > > > > --- a/drivers/block/virtio_blk.c > > > > +++ b/drivers/block/virtio_blk.c > > > > @@ -1026,8 +1026,13 @@ static int init_vq(struct virtio_blk *vblk) > > > > out: > > > > kfree(vqs); > > > > kfree(vqs_info); > > > > - if (err) > > > > + if (err) { > > > > kfree(vblk->vqs); > > > > + /* > > > > + * Set to NULL to prevent freeing vqs again during freezing. > > > > + */ > > > > + vblk->vqs = NULL; > > > > + } > > > > return err; > > > > } > > > > > > > > > > > @@ -1598,6 +1603,12 @@ static int virtblk_freeze_priv(struct virtio_device *vdev) > > > > > > > > vdev->config->del_vqs(vdev); > > > > kfree(vblk->vqs); > > > > + /* > > > > + * Set to NULL to prevent freeing vqs again after a failed vqs > > > > + * allocation during resume. Note that kfree() already handles NULL > > > > + * pointers safely. > > > > + */ > > > > + vblk->vqs = NULL; > > > > > > > > return 0; > > > > } > > > > > > > > --- > > > > base-commit: 8e2755d7779a95dd61d8997ebce33ff8b1efd3fb > > > > change-id: 20250926-virtio_double_free-7ab880d82a17 > > > > > > > > Best regards, > > > > -- > > > > Cong Zhang > > >