* [PATCH v2] virtio-blk: limit seg_max to a safe value
@ 2021-05-24 15:40 Stefan Hajnoczi
2021-05-24 15:47 ` Christoph Hellwig
2021-05-24 20:47 ` Michael S. Tsirkin
0 siblings, 2 replies; 4+ messages in thread
From: Stefan Hajnoczi @ 2021-05-24 15:40 UTC (permalink / raw)
To: linux-block
Cc: Xie Yongji, Christoph Hellwig, Michael S. Tsirkin, jasowang,
Stefan Hajnoczi
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 <stefanha@redhat.com>
---
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
+
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. */
+ /* 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
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] virtio-blk: limit seg_max to a safe value
2021-05-24 15:40 [PATCH v2] virtio-blk: limit seg_max to a safe value Stefan Hajnoczi
@ 2021-05-24 15:47 ` Christoph Hellwig
2021-05-24 20:47 ` Michael S. Tsirkin
1 sibling, 0 replies; 4+ messages in thread
From: Christoph Hellwig @ 2021-05-24 15:47 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: linux-block, Xie Yongji, Christoph Hellwig, Michael S. Tsirkin, jasowang
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 <stefanha@redhat.com>
Looks good,
Reviewed-by: Christoph Hellwig <hch@lst.de>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] virtio-blk: limit seg_max to a safe value
2021-05-24 15:40 [PATCH v2] virtio-blk: limit seg_max to a safe value Stefan Hajnoczi
2021-05-24 15:47 ` Christoph Hellwig
@ 2021-05-24 20:47 ` Michael S. Tsirkin
2021-06-03 14:59 ` Stefan Hajnoczi
1 sibling, 1 reply; 4+ messages in thread
From: Michael S. Tsirkin @ 2021-05-24 20:47 UTC (permalink / raw)
To: Stefan Hajnoczi; +Cc: linux-block, Xie Yongji, Christoph Hellwig, jasowang
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 <stefanha@redhat.com>
> ---
> 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
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] virtio-blk: limit seg_max to a safe value
2021-05-24 20:47 ` Michael S. Tsirkin
@ 2021-06-03 14:59 ` Stefan Hajnoczi
0 siblings, 0 replies; 4+ messages in thread
From: Stefan Hajnoczi @ 2021-06-03 14:59 UTC (permalink / raw)
To: Michael S. Tsirkin; +Cc: linux-block, Xie Yongji, Christoph Hellwig, jasowang
[-- Attachment #1: Type: text/plain, Size: 1661 bytes --]
On Mon, May 24, 2021 at 04:47:37PM -0400, Michael S. Tsirkin wrote:
> 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 <stefanha@redhat.com>
> > ---
> > 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?
Yes.
2^15 = 0x8000 = 32768
> > +
> > 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/
That line is being removed by this patch :).
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^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-05-24 15:40 [PATCH v2] virtio-blk: limit seg_max to a safe value Stefan Hajnoczi
2021-05-24 15:47 ` Christoph Hellwig
2021-05-24 20:47 ` Michael S. Tsirkin
2021-06-03 14:59 ` Stefan Hajnoczi
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