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[Bug 1774336] Re: FS-Cache: Assertion failed: FS-Cache: 6 == 5 is false

 

This bug was fixed in the package linux - 4.13.0-46.51

---------------
linux (4.13.0-46.51) artful; urgency=medium

  * linux: 4.13.0-46.51 -proposed tracker (LP: #1776333)

  * register on binfmt_misc may overflow and crash the system (LP: #1775856)
    - fs/binfmt_misc.c: do not allow offset overflow

  * CVE-2018-11508
    - compat: fix 4-byte infoleak via uninitialized struct field

  * rfi-flush: Switch to new linear fallback flush (LP: #1744173)
    - SAUCE: rfi-flush: Factor out init_fallback_flush()
    - SAUCE: rfi-flush: Move rfi_flush_fallback_area to end of paca
    - powerpc/64s: Improve RFI L1-D cache flush fallback
    - powerpc/rfi-flush: Make it possible to call setup_rfi_flush() again
    - powerpc/rfi-flush: Differentiate enabled and patched flush types
    - powerpc/rfi-flush: Call setup_rfi_flush() after LPM migration

  * Fix enabling bridge MMIO windows (LP: #1771344)
    - powerpc/eeh: Fix enabling bridge MMIO windows

  * CVE-2018-1130
    - dccp: check sk for closed state in dccp_sendmsg()

  * CVE-2018-7757
    - scsi: libsas: fix memory leak in sas_smp_get_phy_events()

  * cpum_sf: ensure sample freq is non-zero (LP: #1772593)
    - s390/cpum_sf: ensure sample frequency of perf event attributes is non-zero

  * wlp3s0: failed to remove key (1, ff:ff:ff:ff:ff:ff) from hardware (-22)
    (LP: #1720930)
    - iwlwifi: mvm: fix "failed to remove key" message

  * CVE-2018-6927
    - futex: Prevent overflow by strengthen input validation

  * After update to 4.13-43 Intel Graphics are Laggy (LP: #1773520)
    - SAUCE: Revert "drm/i915/edp: Allow alternate fixed mode for eDP if
      available."

  * ELANPAD ELAN0612 does not work, patch available (LP: #1773509)
    - SAUCE: Input: elan_i2c - add ELAN0612 to the ACPI table

  * kernel backtrace when receiving large UDP packages (LP: #1772031)
    - iov_iter: fix page_copy_sane for compound pages

  * FS-Cache: Assertion failed: FS-Cache: 6 == 5 is false (LP: #1774336)
    - SAUCE: CacheFiles: fix a read_waiter/read_copier race

  * CVE-2018-5803
    - sctp: verify size of a new chunk in _sctp_make_chunk()

  * enable mic-mute hotkey and led on Lenovo M820z and M920z (LP: #1774306)
    - ALSA: hda/realtek - Enable mic-mute hotkey for several Lenovo AIOs

  * CVE-2018-7755
    - SAUCE: floppy: Do not copy a kernel pointer to user memory in FDGETPRM ioctl

  * CVE-2018-5750
    - ACPI: sbshc: remove raw pointer from printk() message

 -- Khalid Elmously <khalid.elmously@xxxxxxxxxxxxx>  Mon, 11 Jun 2018
23:25:30 +0000

** Changed in: linux (Ubuntu Artful)
       Status: Fix Committed => Fix Released

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-1130

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-11508

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-5750

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-5803

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-6927

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-7755

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-7757

** Changed in: linux (Ubuntu Trusty)
       Status: Fix Committed => Fix Released

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2017-12154

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2017-12193

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2017-15265

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-3665

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https://bugs.launchpad.net/bugs/1774336

Title:
  FS-Cache: Assertion failed: FS-Cache: 6 == 5 is false

Status in linux package in Ubuntu:
  Confirmed
Status in linux source package in Trusty:
  Fix Released
Status in linux source package in Xenial:
  Fix Released
Status in linux source package in Artful:
  Fix Released
Status in linux source package in Bionic:
  Fix Released

Bug description:
  == SRU Justification ==

  [Impact]
  Oops during heavy NFS + FSCache use:

  [81738.886634] FS-Cache: 
  [81738.888281] FS-Cache: Assertion failed
  [81738.889461] FS-Cache: 6 == 5 is false
  [81738.890625] ------------[ cut here ]------------
  [81738.891706] kernel BUG at /build/linux-hVVhWi/linux-4.4.0/fs/fscache/operation.c:494!

  6 == 5 represents an operation being DEAD when it was not expected to
  be.

  [Cause]
  There is a race in fscache and cachefiles. 

  One thread is in cachefiles_read_waiter:
   1) object->work_lock is taken.
   2) the operation is added to the to_do list.
   3) the work lock is dropped.
   4) fscache_enqueue_retrieval is called, which takes a reference.

  Another thread is in cachefiles_read_copier:
   1) object->work_lock is taken
   2) an item is popped off the to_do list.
   3) object->work_lock is dropped.
   4) some processing is done on the item, and fscache_put_retrieval() is called, dropping a reference.

  Now if the this process in cachefiles_read_copier takes place
  *between* steps 3 and 4 in cachefiles_read_waiter, a reference will be
  dropped before it is taken, which leads to the objects reference count
  hitting zero, which leads to lifecycle events for the object happening
  too soon, leading to the assertion failure later on.

  (This is simplified and clarified from the original upstream analysis
  for this patch at https://www.redhat.com/archives/linux-
  cachefs/2018-February/msg00001.html and from a similar patch with a
  different approach to fixing the bug at
  https://www.redhat.com/archives/linux-cachefs/2017-June/msg00002.html)

  [Fix]
  Move fscache_enqueue_retrieval under the lock in cachefiles_read_waiter. This means that the object cannot be popped off the to_do list until it is in a fully consistent state with the reference taken.

  [Testcase]
  A user has run ~100 hours of NFS stress tests and not seen this bug recur.

  [Regression Potential]
   - Limited to fscache/cachefiles. 
   - The change makes things more conservative (doing more under lock) so that's reassuring. 
   - There may be performance impacts but none have been observed so far.

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