CVE-2021-47493

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.