Subject: CVE-2021-47256: mm/memory-failure: make sure wait for page writeback in memory_failure

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

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

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

mm/memory-failure: make sure wait for page writeback in memory_failure

Our syzkaller trigger the "BUG_ON(!list_empty(&inode->i_wb_list))" in
clear_inode:

  kernel BUG at fs/inode.c:519!
  Internal error: Oops - BUG: 0 [#1] SMP
  Modules linked in:
  Process syz-executor.0 (pid: 249, stack limit = 0x00000000a12409d7)
  CPU: 1 PID: 249 Comm: syz-executor.0 Not tainted 4.19.95
  Hardware name: linux,dummy-virt (DT)
  pstate: 80000005 (Nzcv daif -PAN -UAO)
  pc : clear_inode+0x280/0x2a8
  lr : clear_inode+0x280/0x2a8
  Call trace:
    clear_inode+0x280/0x2a8
    ext4_clear_inode+0x38/0xe8
    ext4_free_inode+0x130/0xc68
    ext4_evict_inode+0xb20/0xcb8
    evict+0x1a8/0x3c0
    iput+0x344/0x460
    do_unlinkat+0x260/0x410
    __arm64_sys_unlinkat+0x6c/0xc0
    el0_svc_common+0xdc/0x3b0
    el0_svc_handler+0xf8/0x160
    el0_svc+0x10/0x218
  Kernel panic - not syncing: Fatal exception

A crash dump of this problem show that someone called __munlock_pagevec
to clear page LRU without lock_page: do_mmap -> mmap_region -> do_munmap
-> munlock_vma_pages_range -> __munlock_pagevec.

As a result memory_failure will call identify_page_state without
wait_on_page_writeback.  And after truncate_error_page clear the mapping
of this page.  end_page_writeback won't call sb_clear_inode_writeback to
clear inode->i_wb_list.  That will trigger BUG_ON in clear_inode!

Fix it by checking PageWriteback too to help determine should we skip
wait_on_page_writeback.

The Linux kernel CVE team has assigned CVE-2021-47256 to this issue.

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

	Issue introduced in 3.16 with commit 0bc1f8b0682c and fixed in 4.14.238 with commit d05267fd27a5
	Issue introduced in 3.16 with commit 0bc1f8b0682c and fixed in 4.19.196 with commit 6d210d547adc
	Issue introduced in 3.16 with commit 0bc1f8b0682c and fixed in 5.4.128 with commit 566345aaabac
	Issue introduced in 3.16 with commit 0bc1f8b0682c and fixed in 5.10.46 with commit 9e379da727a7
	Issue introduced in 3.16 with commit 0bc1f8b0682c and fixed in 5.12.13 with commit 28788dc5c705
	Issue introduced in 3.16 with commit 0bc1f8b0682c and fixed in 5.13 with commit e8675d291ac0

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-2021-47256
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:
	mm/memory-failure.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/d05267fd27a5c4f54e06daefa3035995d765ca0c
	https://git.kernel.org/stable/c/6d210d547adc2218ef8b5bcf23518c5f2f1fd872
	https://git.kernel.org/stable/c/566345aaabac853aa866f53a219c4b02a6beb527
	https://git.kernel.org/stable/c/9e379da727a7a031be9b877cde7b9c34a0fb8306
	https://git.kernel.org/stable/c/28788dc5c70597395b6b451dae4549bbaa8e2c56
	https://git.kernel.org/stable/c/e8675d291ac007e1c636870db880f837a9ea112a