[PATCH] iommufd: Fix return value of iommufd_fault_fops_write()

[Zhenzhong Duan]

copy_from_user() may return number of bytes failed to copy, we should
not pass over this number to user space to cheat that write() succeed.
Instead, -EFAULT should be returned.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 07838f7fd529 ("iommufd: Add iommufd fault object")
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxx>
Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 drivers/iommu/iommufd/eventq.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommufd/eventq.c b/drivers/iommu/iommufd/eventq.c
index f1e686b3a265..710eef0b6004 100644
--- a/drivers/iommu/iommufd/eventq.c
+++ b/drivers/iommu/iommufd/eventq.c
@@ -187,9 +187,10 @@ static ssize_t iommufd_fault_fops_write(struct file *filep, const char __user *b
 
 	mutex_lock(&fault->mutex);
 	while (count > done) {
-		rc = copy_from_user(&response, buf + done, response_size);
-		if (rc)
+		if (copy_from_user(&response, buf + done, response_size)) {
+			rc = -EFAULT;
 			break;
+		}
 
 		static_assert((int)IOMMUFD_PAGE_RESP_SUCCESS ==
 			      (int)IOMMU_PAGE_RESP_SUCCESS);
-- 
2.47.3