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

[Joonwon Kang <joonwonkang@google.com>]

[ Upstream commit fcd7f96c783626c07ee3ed75fa3739a8a2052310 ]

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
`fw_xlate` and of_xlate` function pointers, `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.

Cc: stable@vger.kernel.org
Signed-off-by: Joonwon Kang <joonwonkang@google.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
[ changed sp->nargs to sp->args_count in the code and
fw_mbox_index_xlate() to of_mbox_index_xlate() in the commit message. ]
Signed-off-by: Joonwon Kang <joonwonkang@google.com>
---
 drivers/mailbox/mailbox.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index d3d26a2c9895..66cdadbd3d75 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -498,12 +498,10 @@ static struct mbox_chan *
 of_mbox_index_xlate(struct mbox_controller *mbox,
 		    const struct of_phandle_args *sp)
 {
-	int ind = sp->args[0];
-
-	if (ind >= mbox->num_chans)
+	if (sp->args_count < 1 || sp->args[0] >= mbox->num_chans)
 		return ERR_PTR(-EINVAL);
 
-	return &mbox->chans[ind];
+	return &mbox->chans[sp->args[0]];
 }
 
 /**
-- 
2.53.0.473.g4a7958ca14-goog