linux-kernel - Re: [PATCH v1] genirq/msi: fix crash when handling Multi-MSI

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Date:   Mon, 17 Jan 2022 09:59:58 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Tong Zhang <ztong0001@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Gunthorpe <jgg@...pe.ca>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] genirq/msi: fix crash when handling Multi-MSI

On Mon, 17 Jan 2022 09:27:59 +0000,
Tong Zhang <ztong0001@...il.com> wrote:
> 
> pci_msi_domain_check_cap() could return 1 when domain does not support
> multi MSI and user request multi MSI. This positive value will be used by
> __pci_enable_msi_range(). In previous refactor, this positive value is
> handled as error case which will cause kernel crash.
> 
> [    1.197953] BUG: KASAN: use-after-free in __pci_enable_msi_range+0x234/0x320
> [    1.198327] Freed by task 1:
> [    1.198327]  kfree+0x8f/0x2b0
> [    1.198327]  msi_free_msi_descs_range+0xf5/0x130
> [    1.198327]  msi_domain_alloc_irqs_descs_locked+0x8d/0xa0
> [    1.198327]  __pci_enable_msi_range+0x1a4/0x320
> [    1.198327]  pci_alloc_irq_vectors_affinity+0x135/0x1a0
> [    1.198327]  pcie_port_device_register+0x4a1/0x5c0
> [    1.198327]  pcie_portdrv_probe+0x50/0x100

I'm sorry, but you'll have to be a bit clearer in your commit message,
because I cannot relate what you describe with the patch.

The real issue seems to be that a domain_alloc_irqs callback can
return a positive, non-zero value, and I don't think this is expected.

How about this instead? If I am barking up the wrong tree, please
provide a more accurate description of the problem you are seeing.

Thanks,

	M.

diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
index 2bdfce5edafd..da8bb6135627 100644
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -878,8 +878,10 @@ int __msi_domain_alloc_irqs(struct irq_domain *domain, struct device *dev,
 		virq = __irq_domain_alloc_irqs(domain, -1, desc->nvec_used,
 					       dev_to_node(dev), &arg, false,
 					       desc->affinity);
-		if (virq < 0)
-			return msi_handle_pci_fail(domain, desc, allocated);
+		if (virq < 0) {
+			ret = msi_handle_pci_fail(domain, desc, allocated);
+			return ret < 0 ? ret : 0;
+		}
 
 		for (i = 0; i < desc->nvec_used; i++) {
 			irq_set_msi_desc_off(virq, i, desc);

-- 
Without deviation from the norm, progress is not possible.