Cloud Vulnerability DB
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Vulnerability DatabaseCVE-2021-47641
CVE-2021-47641:
Linux Kernel vulnerability analysis and mitigation
Overview
CVE-2021-47641 affects the Linux kernel's cirrusfb driver, specifically related to a divide-by-zero vulnerability in the pixclock handling. The vulnerability was discovered when Syzkaller reported a divide error in cirrusfbcheckpixclock function. The issue occurs in the video framebuffer device (fbdev) subsystem (Kernel Git).
Technical details
The vulnerability exists in the cirrusfbcheckpixclock function where a pixclock value of zero could cause a divide-by-zero error. The issue manifests when processing the PICOS2KHZ conversion of the pixclock value without proper validation. The bug was triggered in the cirrusfbcheckvar function, as evidenced by the call trace showing the execution path through fbsetvar, dofbioctl, and eventually to the system call handler (Kernel Git).
Impact
When triggered, the vulnerability causes a divide error in the kernel, which can lead to a system crash. This was demonstrated in a test environment using QEMU with a standard PC configuration running Linux kernel version 5.15.0-rc6 (Kernel Git).
Mitigation and workarounds
The issue has been fixed by implementing a sanity check on the pixclock value to avoid the divide-by-zero condition. The fix modifies the code to ensure that when the pixclock value is zero, it defaults to 1, and implements a mechanism to round up the pixclock value to get the derived frequency as close to maxclock as possible (Kernel Git).
Additional resources
Source: This report was generated using AI
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