In the quest to remove all stack VLA usage from the kernel[1], this moves the math for cookies calculation into macros and allocates a fixed size array for the maximum number of cookies and adds a runtime sanity check. (Note that the size was always fixed, but just hidden from the compiler.) [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@xxxxxxxxxxxxxx Cc: Jens Axboe <axboe@xxxxxxxxx> Cc: linux-block@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- drivers/block/sunvdc.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/drivers/block/sunvdc.c b/drivers/block/sunvdc.c index 5ca56bfae63c..f68e9baffad7 100644 --- a/drivers/block/sunvdc.c +++ b/drivers/block/sunvdc.c @@ -36,6 +36,10 @@ MODULE_VERSION(DRV_MODULE_VERSION); #define VDC_TX_RING_SIZE 512 #define VDC_DEFAULT_BLK_SIZE 512 +#define MAX_XFER_BLKS (128 * 1024) +#define MAX_XFER_SIZE (MAX_XFER_BLKS / VDC_DEFAULT_BLK_SIZE) +#define MAX_RING_COOKIES ((MAX_XFER_BLKS / PAGE_SIZE) + 2) + #define WAITING_FOR_LINK_UP 0x01 #define WAITING_FOR_TX_SPACE 0x02 #define WAITING_FOR_GEN_CMD 0x04 @@ -450,7 +454,7 @@ static int __send_request(struct request *req) { struct vdc_port *port = req->rq_disk->private_data; struct vio_dring_state *dr = &port->vio.drings[VIO_DRIVER_TX_RING]; - struct scatterlist sg[port->ring_cookies]; + struct scatterlist sg[MAX_RING_COOKIES]; struct vdc_req_entry *rqe; struct vio_disk_desc *desc; unsigned int map_perm; @@ -458,6 +462,9 @@ static int __send_request(struct request *req) u64 len; u8 op; + if (WARN_ON(port->ring_cookies > MAX_RING_COOKIES)) + return -EINVAL; + map_perm = LDC_MAP_SHADOW | LDC_MAP_DIRECT | LDC_MAP_IO; if (rq_data_dir(req) == READ) { @@ -984,9 +991,8 @@ static int vdc_port_probe(struct vio_dev *vdev, const struct vio_device_id *id) goto err_out_free_port; port->vdisk_block_size = VDC_DEFAULT_BLK_SIZE; - port->max_xfer_size = ((128 * 1024) / port->vdisk_block_size); - port->ring_cookies = ((port->max_xfer_size * - port->vdisk_block_size) / PAGE_SIZE) + 2; + port->max_xfer_size = MAX_XFER_SIZE; + port->ring_cookies = MAX_RING_COOKIES; err = vio_ldc_alloc(&port->vio, &vdc_ldc_cfg, port); if (err) -- 2.17.1 -- Kees Cook Pixel Security
