CVE-2021-47540: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47540 is a NULL pointer dereference vulnerability in the Linux kernel's mt76 wireless driver, specifically in the mt7915_get_phy_mode function of the MT7915 PCIe-based chipset driver. The vulnerability was discovered in 2021 and affects Linux kernel versions from 5.8 through 5.10.84 and from 5.11 through 5.15.7 (NVD).

The vulnerability occurs when adding an IBSS (Independent Basic Service Set) interface to the mt7915 driver. The issue stems from an unchecked NULL pointer dereference in the mt7915_get_phy_mode routine, where the code attempts to access the he_cap->has_he field without first verifying that he_cap is not NULL. This results in a kernel NULL pointer dereference at virtual address 0000000000000000, leading to a kernel oops (Kernel Patch). The vulnerability has been assigned a CVSS v3.1 base score of 5.5 (Medium) with vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (NVD).

When exploited, this vulnerability can cause a kernel crash due to the NULL pointer dereference, resulting in a denial of service condition. The impact is limited to availability, with no direct effects on confidentiality or integrity of the system (NVD).

The vulnerability requires local access and can be triggered by attempting to create an IBSS network interface using the affected driver. The exploit conditions are relatively straightforward, requiring low complexity and no user interaction beyond having local access to the system (NVD).

The vulnerability has been fixed through patches that add proper NULL pointer checks before accessing the he_cap structure. The fix involves modifying the mt7915_get_phy_mode function to verify the he_cap pointer before attempting to access its members (Kernel Patch). Users should update to Linux kernel versions that include these fixes.