CVE-2021-47256

MediumCVSS 5.5/10Last modified Jun 17, 2026

Description

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.

Metrics

CVSS 3.1 5.5/10CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected software

VendorProductVersions
LinuxLinux>= 0bc1f8b0682caa39f45ce1e0228ebf43acb46111, < d05267fd27a5c4f54e06daefa3035995d765ca0c; >= 0bc1f8b0682caa39f45ce1e0228ebf43acb46111, < 6d210d547adc2218ef8b5bcf23518c5f2f1fd872; >= 0bc1f8b0682caa39f45ce1e0228ebf43acb46111, < 566345aaabac853aa866f53a219c4b02a6beb527; >= 0bc1f8b0682caa39f45ce1e0228ebf43acb46111, < 9e379da727a7a031be9b877cde7b9c34a0fb8306; >= 0bc1f8b0682caa39f45ce1e0228ebf43acb46111, < 28788dc5c70597395b6b451dae4549bbaa8e2c56; >= 0bc1f8b0682caa39f45ce1e0228ebf43acb46111, < e8675d291ac007e1c636870db880f837a9ea112a
LinuxLinux3.16

References

Timeline

Published
May 21, 2024
Last modified
Jun 17, 2026
NVD status
Analyzed

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CVE-2021-47256: Medium severity, CVSS 5.5 | Vulnix