CVE-2021-47076: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47076 affects the Linux kernel's RDMA/rxe (Remote Direct Memory Access/RoCE) subsystem. The vulnerability was discovered in the kernel versions from 4.8 through 5.12.7, and also affects 5.13-rc1 and 5.13-rc2. The issue stems from RXE missing an update of WQE (Work Queue Element) status in LOCAL_WRITE failures (Kernel Patch).

The vulnerability exists in the RDMA/rxe driver where it fails to properly handle invalid lkey operations. Specifically, when an atomic operation is sent with an explicitly wrong lkey, the system fails to update the WQE status in LOCAL_WRITE failures. This vulnerability has 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).

When exploited, this vulnerability can cause a kernel panic, leading to a denial of service condition. The issue specifically manifests when atomic operations are performed with invalid lkeys, causing system instability and potential service disruption (Kernel Patch).

The vulnerability requires local access and can be triggered through atomic operations with explicitly wrong lkeys in the RDMA/rxe subsystem. A proof-of-concept exists showing how the vulnerability can be triggered using the test_atomic_invalid_lkey test (Kernel Patch).

The vulnerability has been fixed in the Linux kernel through a patch that properly updates the WQE status in case of LOCAL_WRITE failures. The fix includes adding proper error handling by setting wqe->status to IB_WC_LOC_PROT_ERR when invalid lkeys are detected (Kernel Patch).