CVE-2021-47363: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47363 is a division by zero vulnerability in the Linux kernel's nexthop functionality. The issue was discovered in the resilient nexthop group replacement process, where the data path could encounter a resilient nexthop group with zero buckets. This vulnerability was exposed by the resilient nexthop group torture tests in fib_nexthop.sh (Linux Kernel).

The vulnerability occurs when replacing a resilient nexthop group while traffic is being forwarded through it. The tests do not specify the number of buckets during replacement, causing the kernel to allocate a stub resilient table ('struct nh_res_table') with zero buckets. While this table should not be visible to the data path, the old nexthop group might still be used when the stub table is assigned to it, leading to a division by zero condition (Linux Kernel).

When triggered, this vulnerability causes a division by zero error in the kernel, which can lead to a system crash or denial of service condition. The issue affects systems using the Linux kernel's nexthop functionality for network routing (Linux Kernel).

The vulnerability can be triggered during the replacement of resilient nexthop groups while network traffic is being forwarded. It was specifically identified through torture testing using fib_nexthop.sh, suggesting that exploitation requires specific networking configurations and timing (Linux Kernel).

The issue has been fixed by ensuring that the stub table is only assigned to the old nexthop group after confirming that the group is no longer used by the data path. This is accomplished by adding a synchronize_net() call before assigning the stub table (Linux Kernel).