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

From: Greg Kroah-Hartman <[email-masked]>

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.

The Linux kernel CVE team has assigned CVE-2021-47493 to this issue.

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

	Fixed in 5.10.77 with commit 5043fbd294f5
	Fixed in 5.14.16 with commit 2e382600e885
	Fixed in 5.15 with commit 6f1b228529ae

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-2021-47493
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/ocfs2/suballoc.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/5043fbd294f5909a080ade0f04b70a4da9e122b7
	https://git.kernel.org/stable/c/2e382600e8856ea654677b5134ee66e03ea72bc2
	https://git.kernel.org/stable/c/6f1b228529ae49b0f85ab89bcdb6c365df401558