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Tsirkin" To: Stefan Hajnoczi Cc: linux-block@vger.kernel.org, Xie Yongji , Christoph Hellwig , jasowang@redhat.com Subject: Re: [PATCH v2] virtio-blk: limit seg_max to a safe value Message-ID: <20210524164202-mutt-send-email-mst@kernel.org> References: <20210524154020.98195-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210524154020.98195-1-stefanha@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, May 24, 2021 at 04:40:20PM +0100, Stefan Hajnoczi wrote: > The struct virtio_blk_config seg_max value is read from the device and > incremented by 2 to account for the request header and status byte > descriptors added by the driver. > > In preparation for supporting untrusted virtio-blk devices, protect > against integer overflow and limit the value to a safe maximum. > > Signed-off-by: Stefan Hajnoczi > --- > v2: > * Limit to a virtio-specific value instead of using SG_MAX_SEGMENTS > [Christoph] > --- > drivers/block/virtio_blk.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > index b9fa3ef5b57c..1635d4289202 100644 > --- a/drivers/block/virtio_blk.c > +++ b/drivers/block/virtio_blk.c > @@ -21,6 +21,9 @@ > #define VQ_NAME_LEN 16 > #define MAX_DISCARD_SEGMENTS 256u > > +/* The maximum number of sg elements that fit into a virtqueue */ > +#define VIRTIO_BLK_MAX_SG_ELEMS 32768 32768 is what it says for split queues but for packed queues it says 2^15. So 0x8000 then? > + > static int major; > static DEFINE_IDA(vd_index_ida); > > @@ -728,7 +731,10 @@ static int virtblk_probe(struct virtio_device *vdev) > if (err || !sg_elems) > sg_elems = 1; > > - /* We need an extra sg elements at head and tail. */ s/an extra/extra/ > + /* Prevent integer overflows and honor max vq size */ > + sg_elems = min_t(u32, sg_elems, VIRTIO_BLK_MAX_SG_ELEMS - 2); > + > + /* We need extra sg elements at head and tail. */ > sg_elems += 2; > vdev->priv = vblk = kmalloc(sizeof(*vblk), GFP_KERNEL); > if (!vblk) { > -- > 2.31.1 >