[PATCH 5.15.y 2/2] mailbox: qcom-ipcc: fix duplicate channel allocation across holes

[Sasha Levin <sashal@kernel.org>]

From: Anup Vishwakarma <anup.vishwakarma@oss.qualcomm.com>

[ Upstream commit 66c7bcad72430a02c860521031350b84b31ad9a8 ]

The IPCC of_xlate() both scans for a free mailbox channel and checks
for duplicate references to the same underlying IPCC channel. When a
channel has been shutdown it might have left a hole in the channel
list, which would terminate the search without considering duplicates
later in the list.

Continue the traversal of the channel list to detect and reject
duplicates, while keeping track of the first free channel.

Fixes: d6fbfdbc1274 ("mailbox: qcom-ipcc: Fix IPCC mbox channel exhaustion")
Cc: stable@vger.kernel.org
Signed-off-by: Anup Vishwakarma <anup.vishwakarma@oss.qualcomm.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/mailbox/qcom-ipcc.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/mailbox/qcom-ipcc.c b/drivers/mailbox/qcom-ipcc.c
index 10cb0b5461090..b421f84dcfc26 100644
--- a/drivers/mailbox/qcom-ipcc.c
+++ b/drivers/mailbox/qcom-ipcc.c
@@ -164,7 +164,7 @@ static struct mbox_chan *qcom_ipcc_mbox_xlate(struct mbox_controller *mbox,
 {
 	struct qcom_ipcc *ipcc = to_qcom_ipcc(mbox);
 	struct qcom_ipcc_chan_info *mchan;
-	struct mbox_chan *chan;
+	struct mbox_chan *chan, *free_chan = NULL;
 	struct device *dev;
 	int chan_id;
 
@@ -177,16 +177,21 @@ static struct mbox_chan *qcom_ipcc_mbox_xlate(struct mbox_controller *mbox,
 		chan = &ipcc->chans[chan_id];
 		mchan = chan->con_priv;
 
-		if (!mchan)
-			break;
-		else if (mchan->client_id == ph->args[0] &&
-				mchan->signal_id == ph->args[1])
+		if (!mchan) {
+			/* Keep scanning past holes to reject duplicate channel requests. */
+			if (!free_chan)
+				free_chan = chan;
+		} else if (mchan->client_id == ph->args[0] &&
+				mchan->signal_id == ph->args[1]) {
 			return ERR_PTR(-EBUSY);
+		}
 	}
 
-	if (chan_id >= mbox->num_chans)
+	if (!free_chan)
 		return ERR_PTR(-EBUSY);
 
+	chan = free_chan;
+
 	mchan = devm_kzalloc(dev, sizeof(*mchan), GFP_KERNEL);
 	if (!mchan)
 		return ERR_PTR(-ENOMEM);
-- 
2.53.0