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CVE-2021-47493: ocfs2: fix race between searching chunks and release journal_head from buffer_head

• Severity: medium (CVSS 4.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-05-22 · updated 2026-08-04
• Weakness: CWE-362

Description

In the Linux kernel, the following vulnerability has been resolved: ocfs2: fix race between searching chunks and release journal_head from buffer_head Encountered a race between ocfs2_test_bg_bit_allocatable() and jbd2_journal_put_journal_head() resulting in the below vmcore. PID: 106879 TASK: ffff880244ba9c00 CPU: 2 COMMAND: "loop3" Call trace: panic oops_end no_context __bad_area_nosemaphore bad_area_nosemaphore __do_page_fault do_page_fault page_fault [exception RIP: ocfs2_block_group_find_clear_bits+316] ocfs2_block_group_find_clear_bits [ocfs2] ocfs2_cluster_group_search [ocfs2] ocfs2_search_chain [ocfs2] ocfs2_claim_suballoc_bits [ocfs2] __ocfs2_claim_clusters [ocfs2] ocfs2_claim_clusters [ocfs2] ocfs2_local_alloc_slide_window [ocfs2] ocfs2_reserve_local_alloc_bits [ocfs2] ocfs2_reserve_clusters_with_limit [ocfs2] ocfs2_reserve_clusters [ocfs2] ocfs2_lock_refcount_allocators [ocfs2] ocfs2_make_clusters_writable [ocfs2] ocfs2_replace_cow [ocfs2] ocfs2_refcount_cow [ocfs2] ocfs2_file_write_iter [ocfs2] lo_rw_aio loop_queue_work kthread_worker_fn kthread ret_from_fork When ocfs2_test_bg_bit_allocatable() called bh2jh(bg_bh), the bg_bh->b_private NULL as jbd2_journal_put_journal_head() raced and released the jounal head from the buffer head. Needed to take bit lock for the bit 'BH_JournalHead' to fix this race.

Affected products

• Linux kernel: before 5.10.77; from 5.11 before 5.14.16; 5.15-rc1, 5.15-rc2, 5.15-rc3, 5.15-rc4, 5.15-rc5, 5.15-rc6 (+1) — fixed in 5.10.77, 5.14.16

How to fix

Upgrade to a fixed version: Linux kernel 5.10.77, 5.14.16. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/2e382600e8856ea654677b5134ee66e03ea72bc2
• https://git.kernel.org/stable/c/5043fbd294f5909a080ade0f04b70a4da9e122b7
• https://git.kernel.org/stable/c/6f1b228529ae49b0f85ab89bcdb6c365df401558
• https://git.kernel.org/stable/c/2e382600e8856ea654677b5134ee66e03ea72bc2
• https://git.kernel.org/stable/c/5043fbd294f5909a080ade0f04b70a4da9e122b7
• https://git.kernel.org/stable/c/6f1b228529ae49b0f85ab89bcdb6c365df401558

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