Subject: CVE-2024-38582: nilfs2: fix potential hang in nilfs_detach_log_writer()

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

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

nilfs2: fix potential hang in nilfs_detach_log_writer()

Syzbot has reported a potential hang in nilfs_detach_log_writer() called
during nilfs2 unmount.

Analysis revealed that this is because nilfs_segctor_sync(), which
synchronizes with the log writer thread, can be called after
nilfs_segctor_destroy() terminates that thread, as shown in the call trace
below:

nilfs_detach_log_writer
  nilfs_segctor_destroy
    nilfs_segctor_kill_thread  --> Shut down log writer thread
    flush_work
      nilfs_iput_work_func
        nilfs_dispose_list
          iput
            nilfs_evict_inode
              nilfs_transaction_commit
                nilfs_construct_segment (if inode needs sync)
                  nilfs_segctor_sync  --> Attempt to synchronize with
                                          log writer thread
                           *** DEADLOCK ***

Fix this issue by changing nilfs_segctor_sync() so that the log writer
thread returns normally without synchronizing after it terminates, and by
forcing tasks that are already waiting to complete once after the thread
terminates.

The skipped inode metadata flushout will then be processed together in the
subsequent cleanup work in nilfs_segctor_destroy().

The Linux kernel CVE team has assigned CVE-2024-38582 to this issue.

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

	Fixed in 4.19.316 with commit 911d38be1519
	Fixed in 5.4.278 with commit bc9cee50a4a4
	Fixed in 5.10.219 with commit eff7cdf890b0
	Fixed in 5.15.161 with commit 06afce714d87
	Fixed in 6.1.93 with commit 1c3844c5f4ea
	Fixed in 6.6.33 with commit a8799662fed1
	Fixed in 6.8.12 with commit 6e5c8e8e024e
	Fixed in 6.9.3 with commit c516db6ab9ea
	Fixed in 6.10 with commit eb85dace897c

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-2024-38582
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/nilfs2/segment.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/911d38be151921a5d152bb55e81fd752384c6830
	https://git.kernel.org/stable/c/bc9cee50a4a4ca23bdc49f75ea8242d8a2193b3b
	https://git.kernel.org/stable/c/eff7cdf890b02596b8d73e910bdbdd489175dbdb
	https://git.kernel.org/stable/c/06afce714d87c7cd1dcfccbcd800c5c5d2cf1cfd
	https://git.kernel.org/stable/c/1c3844c5f4eac043954ebf6403fa9fd1f0e9c1c0
	https://git.kernel.org/stable/c/a8799662fed1f8747edae87a1937549288baca6a
	https://git.kernel.org/stable/c/6e5c8e8e024e147b834f56f2115aad241433679b
	https://git.kernel.org/stable/c/c516db6ab9eabbedbc430b4f93b0d8728e9b427f
	https://git.kernel.org/stable/c/eb85dace897c5986bc2f36b3c783c6abb8a4292e