CVE-2021-29647: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-29647 is a vulnerability discovered in the Linux kernel before version 5.11.11, specifically in the qrtr_recvmsg function within net/qrtr/qrtr.c. The vulnerability was disclosed on March 30, 2021, affecting the Qualcomm IPC Router (qrtr) implementation. The issue allows attackers to obtain sensitive information from kernel memory due to a partially uninitialized data structure, identified as CID-50535249f624 (NVD, Kernel Commit).

The vulnerability stems from struct sockaddr_qrtr having a 2-byte hole that qrtr_recvmsg() failed to clear before copying kernel data to user space. This uninitialized memory could potentially expose sensitive kernel information when the data structure is passed to userspace. The CVSS v3.1 base score for this vulnerability is 5.5 (Medium), with the vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N (NVD).

The vulnerability allows local attackers to obtain sensitive information from kernel memory. While the impact is limited to information disclosure, the exposed kernel memory could contain sensitive data that might be useful for further attacks (Ubuntu Security).

The vulnerability requires local access to the system and can be exploited through the qrtr_recvmsg function. The attack complexity is low, requiring minimal specialized access conditions. However, it's worth noting that the Qualcomm IPC Router protocol is not enabled in some distributions' official kernel configurations, which limits the exposure (Debian LTS).

The vulnerability was fixed in Linux kernel version 5.11.11 by adding proper memory initialization code to clear the 2-byte hole in the sockaddr_qrtr structure before copying it to userspace. The fix involves using memset to clear the entire structure before setting the specific fields (Kernel Commit). Various distributions have backported this fix to their supported kernel versions, including Fedora, Ubuntu, and Debian (Fedora Update).