Welcome to our detailed breakdown of CVE-2024-41070, a significant cybersecurity issue identified in the Linux kernel. This vulnerability has been classified with a high severity rating and a score of 7.8, indicating a noteworthy risk. Our goal is to provide LinuxPatch customers with a comprehensive understanding of this issue, its implications, and the steps taken to resolve it.
The vulnerability CVE-2024-41070 resides in the Linux kernel, particularly affecting the KVM (Kernel Virtual Machine) module used in conjunction with the POWER9 architecture on systems running the Book3S HV (Hypervisor). Specifically, the issue was found in the kvm_spapr_tce_attach_iommu_group() function.
The root cause of the vulnerability is a use-after-free (UAF) error. Essentially, the function looks up a variable called stt from tablefd, but continues to utilize it after performing an fdput() operation. When fdput() is executed, it leaves tablefd susceptible to being closed by another thread. If another thread closes this file descriptor, it triggers the kvm_spapr_tce_release() and subsequently the release_spapr_tce_table() (via call_rcu()), which results in the freeing of stt.
Although there are protective rcu_read_lock() calls within kvm_spapr_tce_attach_iommu_group(), they were insufficient to prevent the UAF, as stt was used outside the locked regions. The vulnerability was exposed using a test case with an artificial delay introduced right after fdput(), with a user-space program triggering the race condition, leading to the Kernel Address Sanitizer (KASAN) detecting the UAF.
This use-after-free issue could allow malicious entities or programs to execute arbitrary code with kernel privileges. Such an attack could lead to an attacker gaining control over the entire system, data corruption, or loss. Given the nature of the KVM module and its role in handling virtual machines, this vulnerability had the potential to compromise the host machine and all virtual machines running on it.
The resolution involved refining the use of fdput() within the function. The fix introduced a delay in the fdput() operation until stt was no longer being used, which essentially spans the entire duration of the function. To ensure minimal changes and retain functionality, fdput() now gets called at each existing return path within the function.
For future updates, the function may be refactored to adopt a goto or __cleanup style cleanup to prevent similar issues. It is crucial for users and system administrators to apply the latest patches and updates provided by their Linux distribution to mitigate the risk posed by this vulnerability.
LinuxPatch customers should ensure that their systems are consistently updated to the latest kernel versions. Security patches, like the one released for CVE-2024-41070, play a vital role in protecting systems from potential threats. By staying informed and proactive, you can safeguard your systems against such high-severity vulnerabilities.
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