[PATCH v4 2/3] fpga: dfl-afu: validate DMA mapping length in afu_dma_map_region()

[Sebastian Alba Vives <sebasjosue84@gmail.com>]

afu_ioctl_dma_map() accepts a 64-bit length from userspace via
DFL_FPGA_PORT_DMA_MAP ioctl without an upper bound check. The value
is passed to afu_dma_pin_pages() where npages is derived as
length >> PAGE_SHIFT and passed to pin_user_pages_fast() which takes
int nr_pages, causing implicit truncation if length is very large.

Validate map.length at the ioctl entry point before calling
afu_dma_map_region(), rejecting values whose page count exceeds
INT_MAX.

Signed-off-by: Sebastian Alba Vives <sebasjosue84@gmail.com>
---
Changes in v4:
  - Resubmit as full series per maintainer request.
Changes in v3:
  - Move validation to afu_ioctl_dma_map() at the ioctl entry point,
    before crossing the userspace/kernel boundary, instead of deep in
    afu_dma_pin_pages(). Suggested by Greg Kroah-Hartman.
Changes in v2:
  - Added cap at INT_MAX in afu_dma_pin_pages() (superseded by v3).
---
 drivers/fpga/dfl-afu-main.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/fpga/dfl-afu-main.c b/drivers/fpga/dfl-afu-main.c
index 3bf8e73..097a97e 100644
--- a/drivers/fpga/dfl-afu-main.c
+++ b/drivers/fpga/dfl-afu-main.c
@@ -723,6 +723,9 @@ afu_ioctl_dma_map(struct dfl_feature_dev_data *fdata, void __user *arg)
 	if (map.argsz < minsz || map.flags)
 		return -EINVAL;
 
+	if (map.length >> PAGE_SHIFT > (u64)INT_MAX)
+		return -EINVAL;
+
 	ret = afu_dma_map_region(fdata, map.user_addr, map.length, &map.iova);
 	if (ret)
 		return ret;
-- 
2.43.0