Virtualization - Oct 2021 - [PATCH v4 2/2] virtio_ring: check desc == NULL when using indirect with packed

In the case of packed, use indirect desc, since desc is allocated by
kmalloc_array(), we should check whether its return value is NULL.

v4:
   Inside the #2 patch, virtqueue_add_indirect_packed() return -EAGAIN when
   desc == NULL.

v3:
    Update commit message of the #1 patch.

v2:
    Separate the style fix into a single patch.


Xuan Zhuo (2):
  virtio_ring: fix style of virtqueue_add_indirect_packed
  virtio_ring: check desc == NULL when using indirect with packed

 drivers/virtio/virtio_ring.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

--
2.31.0

Align the arguments of virtqueue_add_indirect_packed() to the open ( to
make it look prettier.

Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
Acked-by: Jason Wang <jasowang at redhat.com>
---
 drivers/virtio/virtio_ring.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index dd95dfd85e98..91a46c4da87d 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1050,12 +1050,12 @@ static struct vring_packed_desc
*alloc_indirect_packed(unsigned int total_sg,
 }
 
 static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
-				       struct scatterlist *sgs[],
-				       unsigned int total_sg,
-				       unsigned int out_sgs,
-				       unsigned int in_sgs,
-				       void *data,
-				       gfp_t gfp)
+					 struct scatterlist *sgs[],
+					 unsigned int total_sg,
+					 unsigned int out_sgs,
+					 unsigned int in_sgs,
+					 void *data,
+					 gfp_t gfp)
 {
 	struct vring_packed_desc *desc;
 	struct scatterlist *sg;
-- 
2.31.0

When using indirect with packed, we don't check for allocation failures.
This patch checks that and fall back on direct.

Fixes: 1ce9e6055fa ("virtio_ring: introduce packed ring support")
Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 91a46c4da87d..44a03b6e4dc4 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1065,6 +1065,9 @@ static int virtqueue_add_indirect_packed(struct
vring_virtqueue *vq,
 
 	head = vq->packed.next_avail_idx;
 	desc = alloc_indirect_packed(total_sg, gfp);
+	if (!desc)
+		/* fall back on direct */
+		return -EAGAIN;
 
 	if (unlikely(vq->vq.num_free < 1)) {
 		pr_debug("Can't add buf len 1 - avail = 0\n");
@@ -1176,6 +1179,7 @@ static inline int virtqueue_add_packed(struct virtqueue
*_vq,
 	unsigned int i, n, c, descs_used, err_idx;
 	__le16 head_flags, flags;
 	u16 head, id, prev, curr, avail_used_flags;
+	int err;
 
 	START_USE(vq);
 
@@ -1191,9 +1195,12 @@ static inline int virtqueue_add_packed(struct virtqueue
*_vq,
 
 	BUG_ON(total_sg == 0);
 
-	if (virtqueue_use_indirect(_vq, total_sg))
-		return virtqueue_add_indirect_packed(vq, sgs, total_sg,
-				out_sgs, in_sgs, data, gfp);
+	if (virtqueue_use_indirect(_vq, total_sg)) {
+		err = virtqueue_add_indirect_packed(vq, sgs, total_sg, out_sgs,
+						    in_sgs, data, gfp);
+		if (err != -EAGAIN)
+			return err;
+	}
 
 	head = vq->packed.next_avail_idx;
 	avail_used_flags = vq->packed.avail_used_flags;
-- 
2.31.0

On Tue, Oct 19, 2021 at 07:52:33PM +0800, Xuan Zhuo
wrote:
> In the case of packed, use indirect desc, since desc is allocated by
> kmalloc_array(), we should check whether its return value is NULL.
> 
a better description here:

fix theoretical issues in virtio_ring (so I'm guessing - or did
you observe any null pointer dereferences?)
> v4:
>    Inside the #2 patch, virtqueue_add_indirect_packed() return -EAGAIN when
>    desc == NULL.
> 
> v3:
>     Update commit message of the #1 patch.
> 
> v2:
>     Separate the style fix into a single patch.
> 
> 
> Xuan Zhuo (2):
>   virtio_ring: fix style of virtqueue_add_indirect_packed
>   virtio_ring: check desc == NULL when using indirect with packed
> 
>  drivers/virtio/virtio_ring.c | 25 ++++++++++++++++---------
>  1 file changed, 16 insertions(+), 9 deletions(-)
> 
> --
> 2.31.0