CVE-2021-47295: 
Linux Kernel vulnerability analysis and mitigation

In the Linux kernel, a memory leak vulnerability (CVE-2021-47295) was discovered in the tcindex_set_parms() function. The issue was reported by Syzbot and involves a non-freed perfect hash in tcindex_partial_destroy_work(). When tcindex_set_parms() allocates new tcindex_data and copies fields from the old one, the perfect hash is not properly handled, leading to a memory leak (Kernel Git).

The vulnerability occurs in the net/sched/cls_tcindex.c file where tcindex_partial_destroy_work() fails to properly free the perfect hash data structure. When new tcindex_data is allocated in tcindex_set_parms(), some fields from the old data are copied to the new one, but the perfect hash is not properly handled. Since tcindex_partial_destroy_work() serves as the destroy function for old tcindex_data, the perfect hash needs to be freed to prevent memory leaks (Kernel Git).

The vulnerability results in memory leaks in the Linux kernel's network scheduling subsystem. While memory leaks don't typically allow for code execution, they can lead to resource exhaustion over time, potentially affecting system stability and performance (NVD).

The vulnerability has been assigned a CVSS v3.1 Base Score of 7.5 (HIGH) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, indicating that it can be exploited remotely with no privileges required (NVD).

The vulnerability has been fixed by modifying tcindex_partial_destroy_work() to properly free the perfect hash using tcindex_free_perfect_hash() when p->perfect exists. The fix was implemented in commit f5051bcece50140abd1a11a2d36dc3ec5484fc32 and backported to various stable kernel versions (Kernel Git).