[PATCH] mailbox: bcm74110: Cap rx_svc_init_list growth to prevent PMC-induced OOM

[Danesh Petigara <danesh.petigara@broadcom.com>]

From: Florian Fainelli <florian.fainelli@broadcom.com>

bcm74110_rx_push_init_msg() allocates a GFP_ATOMIC struct for every
BCM_MSG_SVC_INIT word received from the PMC co-processor and appends it
to rx_svc_init_list with no cap on list length.  The only consumers of
this list (bcm74110_rx_pop_init_msg_block / bcm74110_rx_flush_msg) are
called only during probe and at shutdown respectively; after probe
completes, PMC firmware can continuously inject BCM_MSG_SVC_INIT words,
exhausting GFP_ATOMIC reserves and causing a whole-device denial of
service.

Add BCM74110_INIT_MSG_MAX (16 entries) as the maximum list depth.
bcm74110_rx_push_init_msg() now checks the count under the existing
rx_svc_list_lock before allocating; if the cap is reached the message is
dropped and a rate-limited warning is emitted.  The new rx_svc_init_count
field is decremented by bcm74110_rx_pop_init_msg() on successful dequeue
and reset to zero by bcm74110_rx_flush_msg() on shutdown.

Fixes: 52436007b862 ("mailbox: Add support for bcm74110")
Cc: stable@vger.kernel.org
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Assisted-by: Anthropic:claude-sonnet-4.6 cursor
Signed-off-by: Danesh Petigara <danesh.petigara@broadcom.com>
---
 drivers/mailbox/bcm74110-mailbox.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/mailbox/bcm74110-mailbox.c b/drivers/mailbox/bcm74110-mailbox.c
index c8709d509912..bec138d76914 100644
--- a/drivers/mailbox/bcm74110-mailbox.c
+++ b/drivers/mailbox/bcm74110-mailbox.c
@@ -97,6 +97,8 @@ struct bcm74110_mbox_chan {
 	int				type;
 };
 
+#define BCM74110_INIT_MSG_MAX		16
+
 struct bcm74110_mbox {
 	struct platform_device		*pdev;
 	void __iomem			*base;
@@ -105,6 +107,7 @@ struct bcm74110_mbox {
 	int				rx_chan;
 	int				rx_irq;
 	struct list_head		rx_svc_init_list;
+	unsigned int			rx_svc_init_count;
 	spinlock_t			rx_svc_list_lock;
 
 	struct mbox_controller		controller;
@@ -148,7 +151,15 @@ static void bcm74110_rx_push_init_msg(struct bcm74110_mbox *mbox, u32 val)
 	msg->msg = val;
 
 	spin_lock(&mbox->rx_svc_list_lock);
+	if (mbox->rx_svc_init_count >= BCM74110_INIT_MSG_MAX) {
+		spin_unlock(&mbox->rx_svc_list_lock);
+		kfree(msg);
+		dev_warn_ratelimited(&mbox->pdev->dev,
+				     "PMC INIT msg list full, dropping message\n");
+		return;
+	}
 	list_add_tail(&msg->list_entry, &mbox->rx_svc_init_list);
+	mbox->rx_svc_init_count++;
 	spin_unlock(&mbox->rx_svc_list_lock);
 }
 
@@ -225,6 +236,7 @@ static int bcm74110_rx_pop_init_msg(struct bcm74110_mbox *mbox, u32 func_type,
 				 list_entry) {
 		if (BCM_MSG_GET_FIELD(msg->msg, FUNC) == func_type) {
 			list_del(&msg->list_entry);
+			mbox->rx_svc_init_count--;
 			found = true;
 			break;
 		}
@@ -248,6 +260,7 @@ static void bcm74110_rx_flush_msg(struct bcm74110_mbox *mbox)
 
 	spin_lock_irqsave(&mbox->rx_svc_list_lock, flags);
 	list_splice_init(&mbox->rx_svc_init_list, &list_temp);
+	mbox->rx_svc_init_count = 0;
 	spin_unlock_irqrestore(&mbox->rx_svc_list_lock, flags);
 
 	list_for_each_entry_safe(msg, msg_tmp, &list_temp, list_entry) {
-- 
2.54.0