medium CVSS 5.5

CVE-2021-47333·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: misc: alcor_pci: fix null-ptr-deref when there is no PCI bridge There is an issue with the ASPM(optional) capability checking function. A device might be attached to root complex directly, in this case, bus->self(bridge) will be NULL, thus priv->parent_pdev is NULL. Since alcor_pci_init_check_aspm(priv->parent_pdev) checks the PCI link's ASPM capability and populate parent_cap_off, which will be used later by alcor_pci_aspm_ctrl() to dynamically turn on/off device, what we can do here is to avoid checking the capability if we are on the root complex. This will make pdev_cap_off 0 and alcor_pci_aspm_ctrl() will simply return when bring called, effectively disable ASPM for the device. [ 1.246492] BUG: kernel NULL pointer dereference, address: 00000000000000c0 [ 1.248731] RIP: 0010:pci_read_config_byte+0x5/0x40 [ 1.253998] Call Trace: [ 1.254131] ? alcor_pci_find_cap_offset.isra.0+0x3a/0x100 [alcor_pci] [ 1.254476] alcor_pci_probe+0x169/0x2d5 [alcor_pci]

Severity: medium
Software: Kernel
Fixed in: 5.13.4
Published: 2024-05-21

Affected versions

From: 5.13

Until: 5.13.4

Fixed in: 5.13.4

How to fix this CVE

Update your Linux kernel to version 5.13.4 or later to resolve this null pointer dereference vulnerability in the Alcor PCI driver. The issue occurs when a PCI device is directly attached to the root complex without a bridge, causing the ASPM capability check to fail. Systems running kernel versions 5.13.0 through 5.13.3 should prioritize this update to prevent potential kernel crashes.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

Step 1: Check your current kernel version with: uname -r
Step 2: Verify if Alcor PCI device is present on your system by running: lspci | grep -i alcor
Step 3: Search system logs for NULL pointer dereference errors related to alcor_pci: sudo grep -i 'alcor_pci\|null pointer' /var/log/kern.log
Step 4: After patching, confirm the new kernel is loaded with: uname -r and verify it shows 5.13.4 or later

FAQ

What is CVE-2021-47333?

This CVE describes a null pointer dereference flaw in the Linux kernel's Alcor PCI driver that triggers when a PCI device connects directly to the root complex without an intermediate bridge, causing a kernel crash during ASPM capability detection.

Is CVE-2021-47333 being actively exploited?

No, this vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog and no public exploits are available. However, it can cause system instability for affected hardware configurations.

What versions of Kernel are affected by CVE-2021-47333?

Linux kernel versions 5.13.0 through 5.13.3 are vulnerable. The fix was integrated starting with kernel 5.13.4.

How do I check if my server is vulnerable to CVE-2021-47333?

Run 'uname -r' to check your kernel version; if it shows 5.13.0 through 5.13.3 and 'lspci | grep -i alcor' returns results, your system is vulnerable.

Does Defensia detect CVE-2021-47333?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2021-47333 will appear in your dashboard with remediation steps.

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References

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