CVE-2021-3923: 
Linux Kernel vulnerability analysis and mitigation

A flaw was discovered in the Linux kernel's implementation of RDMA (Remote Direct Memory Access) over InfiniBand. The vulnerability, identified as CVE-2021-3923, allows an attacker with a privileged local account to leak kernel stack information when issuing commands to the /dev/infiniband/rdma_cm device node (NVD, Ubuntu Security).

The vulnerability stems from the ibcopyahattrtouser() function, which only initializes 'resp.grh' if the 'resp.isglobal' flag is set. This implementation flaw results in uninitialized stack data being copied to the user, creating an information leak. The vulnerability has been assigned a CVSS v3.1 Base Score of 2.3 (Low) with the vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N (NVD).

While this vulnerability's direct impact is considered low and unlikely to leak sensitive user information, it can potentially be leveraged to defeat existing kernel protection mechanisms. The information leak from kernel stack memory could provide attackers with valuable system information that might be used in further attacks (Redhat Bugzilla).

The vulnerability was fixed in Linux kernel version 5.16. The fix involves zeroing out the whole 'resp' struct to prevent the information leak. Red Hat Enterprise Linux 8 has addressed this vulnerability through kernel updates RHSA-2022:1988 and RHSA-2022:1975 (Redhat Bugzilla, Kernel Patch).