linux-cve-announce - CVE-2021-47637: ubifs: Fix deadlock in concurrent rename whiteout and inode writeback

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Message-ID: <2025022646-CVE-2021-47637-c754@gregkh>
Date: Wed, 26 Feb 2025 02:53:48 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2021-47637: ubifs: Fix deadlock in concurrent rename whiteout and inode writeback

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).

The Linux kernel CVE team has assigned CVE-2021-47637 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.9 with commit 9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 and fixed in 4.19.238 with commit 9dddc8211430fb851ddf0b168e3a00c6f66cc185
	Issue introduced in 4.9 with commit 9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 and fixed in 5.4.189 with commit 37bdf1ad592555ecda1d55b89f6e393e4c0589d1
	Issue introduced in 4.9 with commit 9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 and fixed in 5.10.110 with commit 83e42a78428fc354f5e2049935b84c8d8d29b787
	Issue introduced in 4.9 with commit 9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 and fixed in 5.15.33 with commit c58af8564a7b08757173009030b74baf4b2b762b
	Issue introduced in 4.9 with commit 9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 and fixed in 5.16.19 with commit 70e9090acc32348cedc5def0cd6d5c126efc97b9
	Issue introduced in 4.9 with commit 9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 and fixed in 5.17.2 with commit 8b278c8dcfb565cb65eceb62a38cbf7a7c326db5
	Issue introduced in 4.9 with commit 9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 and fixed in 5.18 with commit afd427048047e8efdedab30e8888044e2be5aa9c

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47637
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/ubifs/dir.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/9dddc8211430fb851ddf0b168e3a00c6f66cc185
	https://git.kernel.org/stable/c/37bdf1ad592555ecda1d55b89f6e393e4c0589d1
	https://git.kernel.org/stable/c/83e42a78428fc354f5e2049935b84c8d8d29b787
	https://git.kernel.org/stable/c/c58af8564a7b08757173009030b74baf4b2b762b
	https://git.kernel.org/stable/c/70e9090acc32348cedc5def0cd6d5c126efc97b9
	https://git.kernel.org/stable/c/8b278c8dcfb565cb65eceb62a38cbf7a7c326db5
	https://git.kernel.org/stable/c/afd427048047e8efdedab30e8888044e2be5aa9c