PCI/MSI: Prevent UAF in error path

When the core MSI allocation fails, then the PCI/MSI code uses an already
freed MSI descriptor to unmask the MSI mask register in order to bring it back
into reset state.

Remove MSI_FLAG_FREE_MSI_DESCS from the PCI/MSI irqdomain flags and let the
PCI/MSI code free the MSI descriptors after usage.

Fixes: 0f62d941acf9 ("genirq/msi: Provide msi_domain_alloc/free_irqs_descs_locked()")
Reported-by: Tong Zhang <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Tested-by: Tong Zhang <[e-mail]>
Acked-by: Bjorn Helgaas <[e-mail]>
Link: https://lore.kernel.org/r/87r1938vbn.ffs@tglx

drivers/pci/msi/irqdomain.c

···
 		msi_domain_free_irqs_descs_locked(domain, &dev->dev);
 	else
 		pci_msi_legacy_teardown_msi_irqs(dev);
+	msi_free_msi_descs(&dev->dev);
 }
 
 /**
···
 	if (info->flags & MSI_FLAG_USE_DEF_CHIP_OPS)
 		pci_msi_domain_update_chip_ops(info);
 
-	info->flags |= MSI_FLAG_ACTIVATE_EARLY | MSI_FLAG_DEV_SYSFS |
-		       MSI_FLAG_FREE_MSI_DESCS;
+	info->flags |= MSI_FLAG_ACTIVATE_EARLY | MSI_FLAG_DEV_SYSFS;
 	if (IS_ENABLED(CONFIG_GENERIC_IRQ_RESERVATION_MODE))
 		info->flags |= MSI_FLAG_MUST_REACTIVATE;
 

drivers/pci/msi/legacy.c

···
 {
 	msi_device_destroy_sysfs(&dev->dev);
 	arch_teardown_msi_irqs(dev);
-	msi_free_msi_descs(&dev->dev);
 }