[PATCH 5/6] dmaengine: idxd: Fix error code handling in idxd_cdev_open()

[Vinicius Costa Gomes]

idxd_cdev_open() mishandles rc on two error paths:

  - On ida_alloc() failure it jumps to failed_ida without setting rc,
    returning the leftover 0 from the earlier successful xa_insert(), so
    open() falsely reports success.

  - When a PASID entry already exists, xa_insert() returns -EBUSY.  This
    is non-fatal and only warned about, but rc is left negative and can
    leak out for a shared wq (which skips the idxd_wq_set_pasid() branch
    that would reset it).

Set rc to the ida_alloc() error before unwinding, and reset rc to 0
after the "PASID already exists" (Fixed the "exist -> exists" typo
while at it) warning.

Fixes: e6fd6d7e5f0f ("dmaengine: idxd: add a device to represent the file opened")
Fixes: b022f59725f0 ("dmaengine: idxd: add idxd_copy_cr() to copy user completion record during page fault handling")
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@xxxxxxxxx>
---
 drivers/dma/idxd/cdev.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/idxd/cdev.c b/drivers/dma/idxd/cdev.c
index 82b07cf942ef..abbab9bdd06c 100644
--- a/drivers/dma/idxd/cdev.c
+++ b/drivers/dma/idxd/cdev.c
@@ -264,8 +264,11 @@ static int idxd_cdev_open(struct inode *inode, struct file *filp)
 		mutex_lock(&wq->uc_lock);
 		rc = xa_insert(&wq->upasid_xa, pasid, ctx, GFP_KERNEL);
 		mutex_unlock(&wq->uc_lock);
-		if (rc < 0)
-			dev_warn(dev, "PASID entry already exist in xarray.\n");
+		if (rc < 0) {
+			/* An existing entry is harmless, warn and continue */
+			dev_warn(dev, "PASID entry already exists in xarray.\n");
+			rc = 0;
+		}
 
 		if (wq_dedicated(wq)) {
 			rc = idxd_wq_set_pasid(wq, pasid);
@@ -279,6 +282,7 @@ static int idxd_cdev_open(struct inode *inode, struct file *filp)
 	idxd_cdev = wq->idxd_cdev;
 	ctx->id = ida_alloc(&file_ida, GFP_KERNEL);
 	if (ctx->id < 0) {
+		rc = ctx->id;
 		dev_warn(dev, "ida alloc failure\n");
 		goto failed_ida;
 	}

-- 
2.56.0