Vulnerabilities > CVE-2021-46982 - Race Condition vulnerability in Linux Kernel
Summary
In the Linux kernel, the following vulnerability has been resolved: f2fs: compress: fix race condition of overwrite vs truncate pos_fsstress testcase complains a panic as belew: ------------[ cut here ]------------ kernel BUG at fs/f2fs/compress.c:1082! invalid opcode: 0000 [#1] SMP PTI CPU: 4 PID: 2753477 Comm: kworker/u16:2 Tainted: G OE 5.12.0-rc1-custom #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014 Workqueue: writeback wb_workfn (flush-252:16) RIP: 0010:prepare_compress_overwrite+0x4c0/0x760 [f2fs] Call Trace: f2fs_prepare_compress_overwrite+0x5f/0x80 [f2fs] f2fs_write_cache_pages+0x468/0x8a0 [f2fs] f2fs_write_data_pages+0x2a4/0x2f0 [f2fs] do_writepages+0x38/0xc0 __writeback_single_inode+0x44/0x2a0 writeback_sb_inodes+0x223/0x4d0 __writeback_inodes_wb+0x56/0xf0 wb_writeback+0x1dd/0x290 wb_workfn+0x309/0x500 process_one_work+0x220/0x3c0 worker_thread+0x53/0x420 kthread+0x12f/0x150 ret_from_fork+0x22/0x30 The root cause is truncate() may race with overwrite as below, so that one reference count left in page can not guarantee the page attaching in mapping tree all the time, after truncation, later find_lock_page() may return NULL pointer. - prepare_compress_overwrite - f2fs_pagecache_get_page - unlock_page - f2fs_setattr - truncate_setsize - truncate_inode_page - delete_from_page_cache - find_lock_page Fix this by avoiding referencing updated page.
Vulnerable Configurations
Common Weakness Enumeration (CWE)
Common Attack Pattern Enumeration and Classification (CAPEC)
- Leveraging Race Conditions This attack targets a race condition occurring when multiple processes access and manipulate the same resource concurrently and the outcome of the execution depends on the particular order in which the access takes place. The attacker can leverage a race condition by "running the race", modifying the resource and modifying the normal execution flow. For instance a race condition can occur while accessing a file, the attacker can trick the system by replacing the original file with his version and cause the system to read the malicious file.
- Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions This attack targets a race condition occurring between the time of check (state) for a resource and the time of use of a resource. The typical example is the file access. The attacker can leverage a file access race condition by "running the race", meaning that he would modify the resource between the first time the target program accesses the file and the time the target program uses the file. During that period of time, the attacker could do something such as replace the file and cause an escalation of privilege.
References
- https://git.kernel.org/stable/c/5639b73fd3bc6fc8ca72e3a9ac15aacaabd7ebff
- https://git.kernel.org/stable/c/5639b73fd3bc6fc8ca72e3a9ac15aacaabd7ebff
- https://git.kernel.org/stable/c/64acb100fe3beb5d20184d0ae3307235bd3555c4
- https://git.kernel.org/stable/c/64acb100fe3beb5d20184d0ae3307235bd3555c4
- https://git.kernel.org/stable/c/936158b15e2648253afb824d252c910c496d34b5
- https://git.kernel.org/stable/c/936158b15e2648253afb824d252c910c496d34b5
- https://git.kernel.org/stable/c/a949dc5f2c5cfe0c910b664650f45371254c0744
- https://git.kernel.org/stable/c/a949dc5f2c5cfe0c910b664650f45371254c0744