Subject: CVE-2021-47463: mm/secretmem: fix NULL page->mapping dereference in page_is_secretmem()

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

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

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

mm/secretmem: fix NULL page->mapping dereference in page_is_secretmem()

Check for a NULL page->mapping before dereferencing the mapping in
page_is_secretmem(), as the page's mapping can be nullified while gup()
is running, e.g.  by reclaim or truncation.

  BUG: kernel NULL pointer dereference, address: 0000000000000068
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: 0000 [#1] PREEMPT SMP NOPTI
  CPU: 6 PID: 4173897 Comm: CPU 3/KVM Tainted: G        W
  RIP: 0010:internal_get_user_pages_fast+0x621/0x9d0
  Code: <48> 81 7a 68 80 08 04 bc 0f 85 21 ff ff 8 89 c7 be
  RSP: 0018:ffffaa90087679b0 EFLAGS: 00010046
  RAX: ffffe3f37905b900 RBX: 00007f2dd561e000 RCX: ffffe3f37905b934
  RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffe3f37905b900
  ...
  CR2: 0000000000000068 CR3: 00000004c5898003 CR4: 00000000001726e0
  Call Trace:
   get_user_pages_fast_only+0x13/0x20
   hva_to_pfn+0xa9/0x3e0
   try_async_pf+0xa1/0x270
   direct_page_fault+0x113/0xad0
   kvm_mmu_page_fault+0x69/0x680
   vmx_handle_exit+0xe1/0x5d0
   kvm_arch_vcpu_ioctl_run+0xd81/0x1c70
   kvm_vcpu_ioctl+0x267/0x670
   __x64_sys_ioctl+0x83/0xa0
   do_syscall_64+0x56/0x80
   entry_SYSCALL_64_after_hwframe+0x44/0xae

The Linux kernel CVE team has assigned CVE-2021-47463 to this issue.

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

	Issue introduced in 5.14 with commit 1507f51255c9 and fixed in 5.14.15 with commit b77ba1e02345
	Issue introduced in 5.14 with commit 1507f51255c9 and fixed in 5.15 with commit 79f9bc584314

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-2021-47463
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:
	include/linux/secretmem.h

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/b77ba1e02345bafd703f0d407bdbd88c3be1f767
	https://git.kernel.org/stable/c/79f9bc5843142b649575f887dccdf1c07ad75c20