CVE-2021-3489: 
Linux Kernel vulnerability analysis and mitigation

The eBPF RINGBUF bpf_ringbuf_reserve() function in the Linux kernel contained a vulnerability (CVE-2021-3489) discovered by Ryota Shiga of Flatt Security. The vulnerability was introduced in Linux kernel version 5.8-rc1 via commit 457f44363a88 and affected kernel versions up to 5.10.37, 5.11.21, and 5.12.4. The issue stemmed from the function not checking that the allocated size was smaller than the ringbuf size (NVD, Ubuntu Security).

The vulnerability existed because the eBPF RINGBUF bpf_ringbuf_reserve() function did not validate that the allocated buffer size was smaller than the ringbuf size. If the consumer pointer was ahead of the producer, a buffer larger than the ringbuf size could be successfully reserved, allowing out-of-bounds memory access. The issue received a CVSS v3.1 base score of 7.8 (High) with vector AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (NVD, Kernel Patch).

Successful exploitation of this vulnerability could allow an attacker to perform out-of-bounds writes within the kernel, potentially leading to arbitrary code execution with kernel privileges. A local attacker could use this to cause a denial of service (system crash) or execute arbitrary code (Ubuntu Security, ZDI Advisory).

The vulnerability requires local access and low privileges to exploit. It was discovered and reported through Trend Micro's Zero Day Initiative by Ryota Shiga of Flatt Security. The vulnerability was demonstrated during Pwn2Own, indicating its practical exploitability (ZDI Advisory, Openwall).

The vulnerability was fixed in Linux kernel version 5.13-rc4 via commit 4b81ccebaeee ('bpf, ringbuf: Deny reserve of buffers larger than ringbuf') and backported to stable kernels in v5.12.4, v5.11.21, and v5.10.37. The fix ensures that the allocating size cannot be larger than the ringbuf size (Kernel Patch, NVD).