# CVE-2021-47256: linux: In the Linux kernel, the following vulnerability has been resolved:  mm/memory-failure: make sure wait for page write...

CVE-2021-47256 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47256, released May 21, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47256
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0023
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 21, 2024

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.10.46-1 | [DEBIAN-CVE-2021-47256](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47256.md) | May 21, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.10.46-1 | [DEBIAN-CVE-2021-47256](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47256.md) | May 21, 2024 |
| Linux | linux Debian 14 | 5.10.46-1 | [DEBIAN-CVE-2021-47256](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47256.md) | May 21, 2024 |

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