s390/pci: fix out of bounds access during irq setup

BugLink: https://bugs.launchpad.net/bugs/1790480

During interrupt setup we allocate interrupt vectors, walk the list of msi
descriptors, and fill in the message data. Requesting more interrupts than
supported on s390 can lead to an out of bounds access.

When we restrict the number of interrupts we should also stop walking the
msi list after all supported interrupts are handled.

Cc: stable@vger.kernel.org
Signed-off-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
(backported from commit 866f3576)
[ kleber: context adjustment ]
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/s390/pci/pci.c

@@ -407,6 +407,8 @@ int arch_setup_msi_irqs(struct pci_dev *pdev, int nvec, int type)
 	hwirq = 0;
 	for_each_pci_msi_entry(msi, pdev) {
 		rc = -EIO;
+		if (hwirq >= msi_vecs)
+			break;
 		irq = irq_alloc_desc(0);	/* Alloc irq on node 0 */
 		if (irq < 0)
 			goto out_msi;