[PATCH v3] mailbox: Prevent out-of-bounds access in of_mbox_index_xlate()

[Joonwon Kang <joonwonkang@google.com>]

Although it is guided that `#mbox-cells` must be at least 1, there are
many instances of `#mbox-cells = <0>;` in the device tree. If that is
the case and the corresponding mailbox controller does not provide
`of_xlate` function pointer, `of_mbox_index_xlate()` will be used by
default and out-of-bounds accesses could occur due to lack of bounds
check in that function.

Signed-off-by: Joonwon Kang <joonwonkang@google.com>
---
 drivers/mailbox/mailbox.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index 5cd8ae222073..5bccdf27d6ab 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -476,7 +476,7 @@ of_mbox_index_xlate(struct mbox_controller *mbox,
 {
 	int ind = sp->args[0];
 
-	if (ind >= mbox->num_chans)
+	if (sp->args_count < 1 || ind >= mbox->num_chans)
 		return ERR_PTR(-EINVAL);
 
 	return &mbox->chans[ind];
-- 
2.51.0.470.ga7dc726c21-goog