CVE-2021-47089: 
Linux Kernel vulnerability analysis and mitigation

In the Linux kernel, a memory leak vulnerability was discovered in the KFENCE (Kernel Electric-Fence) infrastructure when accessing KFENCE objects. The vulnerability was identified by Hulk Robot and assigned CVE-2021-47089. The issue occurs when using the 'cat' command to read KFENCE objects, where memory allocated during the operation is not properly released due to an unimplemented release function in the file operations (Kernel Git).

The vulnerability stems from missing implementation of the release function corresponding to file_operations in KFENCE. When reading KFENCE objects through /sys/kernel/debug/kfence/objects, memory is allocated during seq_open and seq_read_iter operations but not properly freed. The issue can be reproduced by executing 'cat /sys/kernel/debug/kfence/objects' followed by memory leak detection commands. The memory leak occurs in the sequence of operations from do_syscall_64 through full_proxy_open and seq_open, where memory is allocated but not released in the corresponding cleanup path (Kernel Git).

The vulnerability results in memory leaks in the kernel space when accessing KFENCE objects. This can lead to gradual system memory depletion if the affected operations are performed repeatedly (Kernel Git).

The vulnerability can be triggered by any user with access to the KFENCE debug interface through a simple command line operation. The issue is reproducible using the following commands: 'cat /sys/kernel/debug/kfence/objects', 'echo scan > /sys/kernel/debug/kmemleak', and 'cat /sys/kernel/debug/kmemleak' (Kernel Git).

The vulnerability has been fixed by implementing the seq_release function in the file_operations structure for KFENCE objects. The fix involves adding a single line of code to implement the missing release function. Users should update to a patched version of the Linux kernel that includes this fix (Kernel Git).