CVE-2021-46927: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-46927 affects the Linux kernel's nitro_enclaves module. The vulnerability was discovered when a mmap assert was triggered after commit 5b78ed24e8ec ("mm/pagemap: add mmap_assert_locked() annotations to find_vma*()"), causing improper locking behavior. The issue affects Linux kernel versions from 5.15.0 up to (excluding) 5.15.13 (NVD).

The vulnerability occurs in the nitro_enclaves module when calling get_user_pages() without proper locking mechanisms. The issue manifests as a kernel BUG at include/linux/mmap_lock.h:156, triggered by the mmap assert in the find_vma function. The vulnerability has been assigned a CVSS v3.1 Base Score of 5.5 (MEDIUM) with the vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (NVD).

The vulnerability can lead to a kernel panic due to improper locking, potentially causing system availability issues. The CVSS score indicates that while confidentiality and integrity are not affected, there is a high impact on system availability (NVD).

The vulnerability requires local access with low privileges and no user interaction. The attack complexity is low, making it relatively straightforward to exploit for attackers with local access to the system (NVD).

The vulnerability has been patched by replacing get_user_pages() with get_user_pages_unlocked() when setting the enclave memory regions. This fix follows a similar pattern as mmap_read_lock() used together with get_user_pages(). The patch is available in the kernel source tree (Kernel Patch).