Unsynchronized Access to Shared Data in a Multithreaded Context Affecting kernel-debuginfo package, versions <0:4.14.238-182.421.amzn2
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
Do your applications use this vulnerable package?
In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.
Test your applications- Snyk IDSNYK-AMZN2-KERNELDEBUGINFO-8539720
- published20 Dec 2024
- disclosed21 May 2024
Introduced: 21 May 2024
CVE-2021-47256 (opens in a new tab)How to fix?
Upgrade Amazon-Linux:2 kernel-debuginfo to version 0:4.14.238-182.421.amzn2 or higher.
This issue was patched in ALAS2-2021-1685.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-debuginfo package and not the kernel-debuginfo package as distributed by Amazon-Linux.
See How to fix? for Amazon-Linux:2 relevant fixed versions and status.
In the Linux kernel, the following vulnerability has been resolved:
mm/memory-failure: make sure wait for page writeback in memory_failure
Our syzkaller trigger the "BUG_ON(!list_empty(&inode->i_wb_list))" in clear_inode:
kernel BUG at fs/inode.c:519! Internal error: Oops - BUG: 0 [#1] SMP Modules linked in: Process syz-executor.0 (pid: 249, stack limit = 0x00000000a12409d7) CPU: 1 PID: 249 Comm: syz-executor.0 Not tainted 4.19.95 Hardware name: linux,dummy-virt (DT) pstate: 80000005 (Nzcv daif -PAN -UAO) pc : clear_inode+0x280/0x2a8 lr : clear_inode+0x280/0x2a8 Call trace: clear_inode+0x280/0x2a8 ext4_clear_inode+0x38/0xe8 ext4_free_inode+0x130/0xc68 ext4_evict_inode+0xb20/0xcb8 evict+0x1a8/0x3c0 iput+0x344/0x460 do_unlinkat+0x260/0x410 __arm64_sys_unlinkat+0x6c/0xc0 el0_svc_common+0xdc/0x3b0 el0_svc_handler+0xf8/0x160 el0_svc+0x10/0x218 Kernel panic - not syncing: Fatal exception
A crash dump of this problem show that someone called __munlock_pagevec to clear page LRU without lock_page: do_mmap -> mmap_region -> do_munmap -> munlock_vma_pages_range -> __munlock_pagevec.
As a result memory_failure will call identify_page_state without wait_on_page_writeback. And after truncate_error_page clear the mapping of this page. end_page_writeback won't call sb_clear_inode_writeback to clear inode->i_wb_list. That will trigger BUG_ON in clear_inode!
Fix it by checking PageWriteback too to help determine should we skip wait_on_page_writeback.
References
- http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-47256
- https://git.kernel.org/stable/c/28788dc5c70597395b6b451dae4549bbaa8e2c56
- https://git.kernel.org/stable/c/566345aaabac853aa866f53a219c4b02a6beb527
- https://git.kernel.org/stable/c/6d210d547adc2218ef8b5bcf23518c5f2f1fd872
- https://git.kernel.org/stable/c/9e379da727a7a031be9b877cde7b9c34a0fb8306
- https://git.kernel.org/stable/c/d05267fd27a5c4f54e06daefa3035995d765ca0c
- https://git.kernel.org/stable/c/e8675d291ac007e1c636870db880f837a9ea112a