# CVE-2021-47492: linux: In the Linux kernel, the following vulnerability has been resolved:  mm, thp: bail out early in collapse_file for wri...

CVE-2021-47492 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47492, released May 22, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47492
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0022
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 22, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  mm, thp: bail out early in collapse_file for writeback page  Currently collapse_file does not explicitly check PG_writeback, instead, page_has_private and try_to_release_page are used to filter writeback pages.  This does not work for xfs with blocksize equal to or larger than pagesize, because in such case xfs has no page->private.  This makes collapse_file bail out early for writeback page.  Otherwise, xfs end_page_writeback will panic as follows.    page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:ffff0003f88c86a8 index:0x0 pfn:0x84ef32   aops:xfs_address_space_operations [xfs] ino:30000b7 dentry name:"libtest.so"   flags: 0x57fffe0000008027(locked|referenced|uptodate|active|writeback)   raw: 57fffe0000008027 ffff80001b48bc28 ffff80001b48bc28 ffff0003f88c86a8   raw: 0000000000000000 0000000000000000 00000000ffffffff ffff0000c3e9a000   page dumped because: VM_BUG_ON_PAGE(((unsigned int) page_ref_count(page) + 127u <= 127u))   page->mem_cgroup:ffff0000c3e9a000   ------------[ cut here ]------------   kernel BUG at include/linux/mm.h:1212!   Internal error: Oops - BUG: 0 [#1] SMP   Modules linked in:   BUG: Bad page state in process khugepaged  pfn:84ef32    xfs(E)   page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:0 index:0x0 pfn:0x84ef32    libcrc32c(E) rfkill(E) aes_ce_blk(E) crypto_simd(E) ...   CPU: 25 PID: 0 Comm: swapper/25 Kdump: loaded Tainted: ...   pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--)   Call trace:     end_page_writeback+0x1c0/0x214     iomap_finish_page_writeback+0x13c/0x204     iomap_finish_ioend+0xe8/0x19c     iomap_writepage_end_bio+0x38/0x50     bio_endio+0x168/0x1ec     blk_update_request+0x278/0x3f0     blk_mq_end_request+0x34/0x15c     virtblk_request_done+0x38/0x74 [virtio_blk]     blk_done_softirq+0xc4/0x110     __do_softirq+0x128/0x38c     __irq_exit_rcu+0x118/0x150     irq_exit+0x1c/0x30     __handle_domain_irq+0x8c/0xf0     gic_handle_irq+0x84/0x108     el1_irq+0xcc/0x180     arch_cpu_idle+0x18/0x40     default_idle_call+0x4c/0x1a0     cpuidle_idle_call+0x168/0x1e0     do_idle+0xb4/0x104     cpu_startup_entry+0x30/0x9c     secondary_start_kernel+0x104/0x180   Code: d4210000 b0006161 910c8021 94013f4d (d4210000)   ---[ end trace 4a88c6a074082f8c ]---   Kernel panic - not syncing: Oops - BUG: Fatal exception in interrupt

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.15.3-1 | [DEBIAN-CVE-2021-47492](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47492.md) | May 22, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.15.3-1 | [DEBIAN-CVE-2021-47492](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47492.md) | May 22, 2024 |
| Linux | linux Debian 14 | 5.15.3-1 | [DEBIAN-CVE-2021-47492](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47492.md) | May 22, 2024 |

---

Data as of 2026-11-09T07:25:28Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.