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Muchun Song 5126bdeaf9 mm/ksm: fix NULL pointer dereference when KSM zero page is enabled 
commit 56df70a63e upstream.

find_mergeable_vma() can return NULL.  In this case, it leads to a crash
when we access vm_mm(its offset is 0x40) later in write_protect_page.
And this case did happen on our server.  The following call trace is
captured in kernel 4.19 with the following patch applied and KSM zero
page enabled on our server.

  commit e86c59b1b1 ("mm/ksm: improve deduplication of zero pages with colouring")

So add a vma check to fix it.

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000040
  Oops: 0000 [#1] SMP NOPTI
  CPU: 9 PID: 510 Comm: ksmd Kdump: loaded Tainted: G OE 4.19.36.bsk.9-amd64 #4.19.36.bsk.9
  RIP: try_to_merge_one_page+0xc7/0x760
  Code: 24 58 65 48 33 34 25 28 00 00 00 89 e8 0f 85 a3 06 00 00 48 83 c4
        60 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 8b 46 08 a8 01 75 b8 <49>
        8b 44 24 40 4c 8d 7c 24 20 b9 07 00 00 00 4c 89 e6 4c 89 ff 48
  RSP: 0018:ffffadbdd9fffdb0 EFLAGS: 00010246
  RAX: ffffda83ffd4be08 RBX: ffffda83ffd4be40 RCX: 0000002c6e800000
  RDX: 0000000000000000 RSI: ffffda83ffd4be40 RDI: 0000000000000000
  RBP: ffffa11939f02ec0 R08: 0000000094e1a447 R09: 00000000abe76577
  R10: 0000000000000962 R11: 0000000000004e6a R12: 0000000000000000
  R13: ffffda83b1e06380 R14: ffffa18f31f072c0 R15: ffffda83ffd4be40
  FS: 0000000000000000(0000) GS:ffffa0da43b80000(0000) knlGS:0000000000000000
  CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000040 CR3: 0000002c77c0a003 CR4: 00000000007626e0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  PKRU: 55555554
  Call Trace:
    ksm_scan_thread+0x115e/0x1960
    kthread+0xf5/0x130
    ret_from_fork+0x1f/0x30

[songmuchun@bytedance.com: if the vma is out of date, just exit]
  Link: http://lkml.kernel.org/r/20200416025034.29780-1-songmuchun@bytedance.com
[akpm@linux-foundation.org: add the conventional braces, replace /** with /*]
Fixes: e86c59b1b1 ("mm/ksm: improve deduplication of zero pages with colouring")
Co-developed-by: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Cc: Markus Elfring <Markus.Elfring@web.de>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200416025034.29780-1-songmuchun@bytedance.com
Link: http://lkml.kernel.org/r/20200414132905.83819-1-songmuchun@bytedance.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2020-04-29 16:33:15 +02:00
Documentation USB: hub: Revert commit bd0e6c9614 ("usb: hub: try old enumeration scheme first for high speed devices") 2020-04-29 16:33:14 +02:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch powerpc/pseries: Fix MCE handling on pseries 2020-04-29 16:33:01 +02:00
block block, bfq: invoke flush_idle_tree after reparent_active_queues in pd_offline 2020-04-23 10:36:26 +02:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: rng - Fix a refcounting bug in crypto_rng_reset() 2020-04-17 10:50:16 +02:00
drivers staging: gasket: Fix incongruency in handling of sysfs entries creation 2020-04-29 16:33:14 +02:00
fs coredump: fix null pointer dereference on coredump 2020-04-29 16:33:14 +02:00
include vmalloc: fix remap_vmalloc_range() bounds checks 2020-04-29 16:33:14 +02:00
init kbuild: remove header compile test 2020-03-05 16:43:47 +01:00
ipc ipc/util.c: sysvipc_find_ipc() should increase position index 2020-04-29 16:33:00 +02:00
kernel perf/core: Disable page faults when getting phys address 2020-04-29 16:33:02 +02:00
lib lib/raid6/test: fix build on distros whose /bin/sh is not bash 2020-04-29 16:33:00 +02:00
mm mm/ksm: fix NULL pointer dereference when KSM zero page is enabled 2020-04-29 16:33:15 +02:00
net xfrm: Always set XFRM_TRANSFORMED in xfrm{4,6}_output_finish 2020-04-29 16:33:11 +02:00
samples vmalloc: fix remap_vmalloc_range() bounds checks 2020-04-29 16:33:14 +02:00
scripts kconfig: qconf: Fix a few alignment issues 2020-04-29 16:33:00 +02:00
security KEYS: Avoid false positive ENOMEM error on key read 2020-04-29 16:33:11 +02:00
sound ALSA: usb-audio: Add connector notifier delegation 2020-04-29 16:33:12 +02:00
tools selftests: Fix suppress test in fib_tests.sh 2020-04-29 16:33:09 +02:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt KVM: Check for a bad hva before dropping into the ghc slow path 2020-03-05 16:43:48 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 17:22:19 +01:00
Makefile Linux 5.4.35 2020-04-23 10:36:46 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.