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9933bfb6d3
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Thomas Gleixner 9933bfb6d3 futex: Cure exit race 
commit da791a6675 upstream.

Stefan reported, that the glibc tst-robustpi4 test case fails
occasionally. That case creates the following race between
sys_exit() and sys_futex_lock_pi():

 CPU0				CPU1

 sys_exit()			sys_futex()
  do_exit()			 futex_lock_pi()
   exit_signals(tsk)		  No waiters:
    tsk->flags |= PF_EXITING;	  *uaddr == 0x00000PID
  mm_release(tsk)		  Set waiter bit
   exit_robust_list(tsk) {	  *uaddr = 0x80000PID;
      Set owner died		  attach_to_pi_owner() {
    *uaddr = 0xC0000000;	   tsk = get_task(PID);
   }				   if (!tsk->flags & PF_EXITING) {
  ...				     attach();
  tsk->flags |= PF_EXITPIDONE;	   } else {
				     if (!(tsk->flags & PF_EXITPIDONE))
				       return -EAGAIN;
				     return -ESRCH; <--- FAIL
				   }

ESRCH is returned all the way to user space, which triggers the glibc test
case assert. Returning ESRCH unconditionally is wrong here because the user
space value has been changed by the exiting task to 0xC0000000, i.e. the
FUTEX_OWNER_DIED bit is set and the futex PID value has been cleared. This
is a valid state and the kernel has to handle it, i.e. taking the futex.

Cure it by rereading the user space value when PF_EXITING and PF_EXITPIDONE
is set in the task which 'owns' the futex. If the value has changed, let
the kernel retry the operation, which includes all regular sanity checks
and correctly handles the FUTEX_OWNER_DIED case.

If it hasn't changed, then return ESRCH as there is no way to distinguish
this case from malfunctioning user space. This happens when the exiting
task did not have a robust list, the robust list was corrupted or the user
space value in the futex was simply bogus.

Reported-by: Stefan Liebler <stli@linux.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: stable@vger.kernel.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=200467
Link: https://lkml.kernel.org/r/20181210152311.986181245@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2018-12-29 13:37:57 +01:00
arch KVM: Fix UAF in nested posted interrupt processing 2018-12-29 13:37:56 +01:00
block block/bio: Do not zero user pages 2018-12-19 19:19:50 +01:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: do not free algorithm before using 2018-12-13 09:16:21 +01:00
Documentation x86/speculation: Provide IBPB always command line options 2018-12-05 19:32:04 +01:00
drivers Drivers: hv: vmbus: Return -EINVAL for the sys files for unopened channels 2018-12-29 13:37:56 +01:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs ubifs: Handle re-linking of inodes correctly while recovery 2018-12-29 13:37:55 +01:00
include scsi: t10-pi: Return correct ref tag when queue has no integrity profile 2018-12-29 13:37:55 +01:00
init sched/pelt: Fix warning and clean up IRQ PELT config 2018-12-19 19:19:49 +01:00
ipc ipc/shm.c: use ERR_CAST() for shm_lock() error return 2018-10-05 16:32:04 -07:00
kernel futex: Cure exit race 2018-12-29 13:37:57 +01:00
lib debugobjects: avoid recursive calls with kmemleak 2018-12-17 09:24:41 +01:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm/page_alloc.c: fix calculation of pgdat->nr_zones 2018-12-17 09:24:40 +01:00
net SUNRPC: Fix a potential race in xprt_connect() 2018-12-21 14:15:17 +01:00
samples samples: disable CONFIG_SAMPLES for UML 2018-10-11 02:15:46 +09:00
scripts scripts/spdxcheck.py: always open files in binary mode 2018-12-19 19:19:50 +01:00
security selinux: add support for RTM_NEWCHAIN, RTM_DELCHAIN, and RTM_GETCHAIN 2018-12-08 12:59:08 +01:00
sound ALSA: hda/realtek - Fix the mute LED regresion on Lenovo X1 Carbon 2018-12-17 09:24:42 +01:00
tools tools/testing/nvdimm: Align test resources to 128M 2018-12-21 14:15:23 +01:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: arm64: Fix caching of host MDCR_EL2 value 2018-11-13 11:08:47 -08:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS MAINTAINERS: Add Sasha as a stable branch maintainer 2018-12-01 09:37:25 +01:00
Makefile Linux 4.19.12 2018-12-21 14:15:25 +01:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.