dmaengine: idxd: Fix allowing write() from different address spaces

Check if the process submitting the descriptor belongs to the same
address space as the one that opened the file, reject otherwise.

Fixes: 6827738 ("dmaengine: idxd: add a write() method for applications to submit work")
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/20250421170337.3008875-1-dave.jiang@intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/idxd/cdev.c

@@ -407,6 +407,9 @@ static int idxd_cdev_mmap(struct file *filp, struct vm_area_struct *vma)
 	if (!idxd->user_submission_safe && !capable(CAP_SYS_RAWIO))
 		return -EPERM;
 
+	if (current->mm != ctx->mm)
+		return -EPERM;
+
 	rc = check_vma(wq, vma, __func__);
 	if (rc < 0)
 		return rc;
@@ -473,6 +476,9 @@ static ssize_t idxd_cdev_write(struct file *filp, const char __user *buf, size_t
 	ssize_t written = 0;
 	int i;
 
+	if (current->mm != ctx->mm)
+		return -EPERM;
+
 	for (i = 0; i < len/sizeof(struct dsa_hw_desc); i++) {
 		int rc = idxd_submit_user_descriptor(ctx, udesc + i);
 
@@ -493,6 +499,9 @@ static __poll_t idxd_cdev_poll(struct file *filp,
 	struct idxd_device *idxd = wq->idxd;
 	__poll_t out = 0;
 
+	if (current->mm != ctx->mm)
+		return -EPERM;
+
 	poll_wait(filp, &wq->err_queue, wait);
 	spin_lock(&idxd->dev_lock);
 	if (idxd->sw_err.valid)