ata: libahci_platform: Sanity check the DT child nodes number

Having greater than AHCI_MAX_PORTS (32) ports detected isn't that critical
from the further AHCI-platform initialization point of view since
exceeding the ports upper limit will cause allocating more resources than
will be used afterwards. But detecting too many child DT-nodes doesn't
seem right since it's very unlikely to have it on an ordinary platform. In
accordance with the AHCI specification there can't be more than 32 ports
implemented at least due to having the CAP.NP field of 5 bits wide and the
PI register of dword size. Thus if such situation is found the DTB must
have been corrupted and the data read from it shouldn't be reliable. Let's
consider that as an erroneous situation and halt further resources
allocation.

Note it's logically more correct to have the nports set only after the
initialization value is checked for being sane. So while at it let's make
sure nports is assigned with a correct value.
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

drivers/ata/libahci_platform.c

@@ -450,14 +450,24 @@ struct ahci_host_priv *ahci_platform_get_resources(struct platform_device *pdev,
 		}
 	}
 
-	hpriv->nports = child_nodes = of_get_child_count(dev->of_node);
+	/*
+	 * Too many sub-nodes most likely means having something wrong with
+	 * the firmware.
+	 */
+	child_nodes = of_get_child_count(dev->of_node);
+	if (child_nodes > AHCI_MAX_PORTS) {
+		rc = -EINVAL;
+		goto err_out;
+	}
 
 	/*
 	 * If no sub-node was found, we still need to set nports to
 	 * one in order to be able to use the
 	 * ahci_platform_[en|dis]able_[phys|regulators] functions.
 	 */
-	if (!child_nodes)
+	if (child_nodes)
+		hpriv->nports = child_nodes;
+	else
 		hpriv->nports = 1;
 
 	hpriv->phys = devm_kcalloc(dev, hpriv->nports, sizeof(*hpriv->phys), GFP_KERNEL);