CVE-2021-47229 PCI: aardvark: Fix kernel panic during PIO transfer

What is CVE-2021-47229?

CVE-2021-47229 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

PCI: aardvark: Fix kernel panic during PIO transfer

Trying to start a new PIO transfer by writing value 0 in PIO_START register when previous transfer has not yet completed (which is indicated by value 1 in PIO_START) causes an External Abort on CPU, which results in kernel panic:

SError Interrupt on CPU0, code 0xbf000002 -- SError Kernel panic - not syncing: Asynchronous SError Interrupt

To prevent kernel panic, it is required to reject a new PIO transfer when previous one has not finished yet.

If previous PIO transfer is not finished yet, the kernel may issue a new PIO request only if the previous PIO transfer timed out.

In the past the root cause of this issue was incorrectly identified (as it often happens during link retraining or after link down event) and special hack was implemented in Trusted Firmware to catch all SError events in EL3, to ignore errors with code 0xbf000002 and not forwarding any other errors to kernel and instead throw panic from EL3 Trusted Firmware handler.

Links to discussion and patches about this issue: https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/commit/?id=3c7dcdac5c50 https://lore.kernel.org/linux-pci/[email protected]/ https://lore.kernel.org/linux-pci/[email protected]/ https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/1541

But the real cause was the fact that during link retraining or after link down event the PIO transfer may take longer time, up to the 1.44s until it times out. This increased probability that a new PIO transfer would be issued by kernel while previous one has not finished yet.

After applying this change into the kernel, it is possible to revert the mentioned TF-A hack and SError events do not have to be caught in TF-A EL3.

Which versions are affected by CVE-2021-47229?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2021-47229?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2021-47229 being exploited?

There is no known exploitation of CVE-2021-47229 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2021-47229, GHSA-74hg-7r85-vvw3, UBUNTU-CVE-2021-47229.