vulnerability

Ubuntu: (CVE-2021-47637): linux vulnerability

Severity
6
CVSS
(AV:L/AC:L/Au:S/C:N/I:C/A:C)
Published
Feb 26, 2025
Added
Mar 3, 2025
Modified
Jun 10, 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)
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).

Solution(s)

ubuntu-upgrade-linuxubuntu-upgrade-linux-awsubuntu-upgrade-linux-aws-5-4ubuntu-upgrade-linux-aws-fipsubuntu-upgrade-linux-aws-hweubuntu-upgrade-linux-azureubuntu-upgrade-linux-azure-4-15ubuntu-upgrade-linux-azure-5-15ubuntu-upgrade-linux-azure-5-4ubuntu-upgrade-linux-azure-fipsubuntu-upgrade-linux-bluefieldubuntu-upgrade-linux-fipsubuntu-upgrade-linux-gcpubuntu-upgrade-linux-gcp-4-15ubuntu-upgrade-linux-gcp-5-4ubuntu-upgrade-linux-gcp-fipsubuntu-upgrade-linux-gkeubuntu-upgrade-linux-hweubuntu-upgrade-linux-hwe-5-15ubuntu-upgrade-linux-hwe-5-4ubuntu-upgrade-linux-ibmubuntu-upgrade-linux-ibm-5-4ubuntu-upgrade-linux-intel-iotgubuntu-upgrade-linux-intel-iotg-5-15ubuntu-upgrade-linux-iotubuntu-upgrade-linux-kvmubuntu-upgrade-linux-lowlatencyubuntu-upgrade-linux-lowlatency-hwe-5-15ubuntu-upgrade-linux-oracleubuntu-upgrade-linux-oracle-5-4ubuntu-upgrade-linux-raspiubuntu-upgrade-linux-raspi-5-4ubuntu-upgrade-linux-realtime
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