# CVE-2021-47637: linux: In the Linux kernel, the following vulnerability has been resolved:  ubifs: Fix deadlock in concurrent rename whiteou...

CVE-2021-47637 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47637, released February 26, 2025. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47637
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0019
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Feb 26, 2025

## Description

In the Linux kernel, the following vulnerability has been resolved:  ubifs: Fix deadlock in concurrent rename whiteout and inode writeback  Following hung tasks: [   77.028764] task:kworker/u8:4    state:D stack:    0 pid:  132 [   77.028820] Call Trace: [   77.029027]  schedule+0x8c/0x1b0 [   77.029067]  mutex_lock+0x50/0x60 [   77.029074]  ubifs_write_inode+0x68/0x1f0 [ubifs] [   77.029117]  __writeback_single_inode+0x43c/0x570 [   77.029128]  writeback_sb_inodes+0x259/0x740 [   77.029148]  wb_writeback+0x107/0x4d0 [   77.029163]  wb_workfn+0x162/0x7b0  [   92.390442] task:aa              state:D stack:    0 pid: 1506 [   92.390448] Call Trace: [   92.390458]  schedule+0x8c/0x1b0 [   92.390461]  wb_wait_for_completion+0x82/0xd0 [   92.390469]  __writeback_inodes_sb_nr+0xb2/0x110 [   92.390472]  writeback_inodes_sb_nr+0x14/0x20 [   92.390476]  ubifs_budget_space+0x705/0xdd0 [ubifs] [   92.390503]  do_rename.cold+0x7f/0x187 [ubifs] [   92.390549]  ubifs_rename+0x8b/0x180 [ubifs] [   92.390571]  vfs_rename+0xdb2/0x1170 [   92.390580]  do_renameat2+0x554/0x770  , are caused by concurrent rename whiteout and inode writeback processes: 	rename_whiteout(Thread 1)	        wb_workfn(Thread2) ubifs_rename   do_rename     lock_4_inodes (Hold ui_mutex)     ubifs_budget_space       make_free_space         shrink_liability 	  __writeback_inodes_sb_nr 	    bdi_split_work_to_wbs (Queue new wb work) 					      wb_do_writeback(wb work) 						__writeback_single_inode 					          ubifs_write_inode 					            LOCK(ui_mutex) 							   ↑ 	      wb_wait_for_completion (Wait wb work) <-- deadlock!  Reproducer (Detail program in [Link]):   1. SYS_renameat2("/mp/dir/file", "/mp/dir/whiteout", RENAME_WHITEOUT)   2. Consume out of space before kernel(mdelay) doing budget for whiteout  Fix it by doing whiteout space budget before locking ubifs inodes. BTW, it also fixes wrong goto tag 'out_release' in whiteout budget error handling path(It should at least recover dir i_size and unlock 4 ubifs inodes).

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.17.3-1 | [DEBIAN-CVE-2021-47637](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47637.md) | Feb 26, 2025 |
| Linux | linux Debian 13.5 (trixie) | 5.17.3-1 | [DEBIAN-CVE-2021-47637](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47637.md) | Feb 26, 2025 |
| Linux | linux Debian 14 | 5.17.3-1 | [DEBIAN-CVE-2021-47637](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47637.md) | Feb 26, 2025 |

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Data as of 2026-11-08T19:12:23Z 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

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