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Oleg Nesterov 138e4ad67a epoll: fix race between ep_poll_callback(POLLFREE) and ep_free()/ep_remove() 
The race was introduced by me in commit 971316f050 ("epoll:
ep_unregister_pollwait() can use the freed pwq->whead").  I did not
realize that nothing can protect eventpoll after ep_poll_callback() sets
->whead = NULL, only whead->lock can save us from the race with
ep_free() or ep_remove().

Move ->whead = NULL to the end of ep_poll_callback() and add the
necessary barriers.

TODO: cleanup the ewake/EPOLLEXCLUSIVE logic, it was confusing even
before this patch.

Hopefully this explains use-after-free reported by syzcaller:

	BUG: KASAN: use-after-free in debug_spin_lock_before
	...
	 _raw_spin_lock_irqsave+0x4a/0x60 kernel/locking/spinlock.c:159
	 ep_poll_callback+0x29f/0xff0 fs/eventpoll.c:1148

this is spin_lock(eventpoll->lock),

	...
	Freed by task 17774:
	...
	 kfree+0xe8/0x2c0 mm/slub.c:3883
	 ep_free+0x22c/0x2a0 fs/eventpoll.c:865

Fixes: 971316f050 ("epoll: ep_unregister_pollwait() can use the freed pwq->whead")
Reported-by: 范龙飞 <long7573@126.com>
Cc: stable@vger.kernel.org
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-09-01 13:07:35 -07:00
arch Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux 2017-09-01 10:36:22 -07:00
block blk-mq-debugfs: Add names for recently added flags 2017-08-25 08:07:44 -06:00
certs modsign: add markers to endif-statements in certs/Makefile 2017-07-14 11:01:37 +10:00
crypto crypto: algif_skcipher - only call put_page on referenced and used pages 2017-08-22 14:45:48 +08:00
Documentation Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-08-21 13:16:27 -07:00
drivers Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-09-01 12:49:03 -07:00
firmware firmware/Makefile: force recompilation if makefile changes 2017-05-08 17:15:10 -07:00
fs epoll: fix race between ep_poll_callback(POLLFREE) and ep_free()/ep_remove() 2017-09-01 13:07:35 -07:00
include Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-09-01 12:49:03 -07:00
init random: do not ignore early device randomness 2017-07-12 16:26:00 -07:00
ipc ipc: add missing container_of()s for randstruct 2017-08-02 17:16:12 -07:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-09-01 12:49:03 -07:00
lib Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2017-09-01 10:30:03 -07:00
mm Merge branch 'akpm' (patches from Andrew) 2017-08-31 17:56:56 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-09-01 12:49:03 -07:00
samples samples/bpf: fix bpf tunnel cleanup 2017-07-31 22:02:47 -07:00
scripts scripts/dtc: fix '%zx' warning 2017-08-31 16:33:15 -07:00
security Now that IPC and other changes have landed, enable manual markings for 2017-07-19 08:55:18 -07:00
sound ASoC: Fixes for v4.13 2017-08-31 14:08:26 +02:00
tools NTB bug fixes to address an incorrect ntb_mw_count reference in the NTB 2017-08-27 17:01:54 -07:00
usr ramfs: clarify help text that compression applies to ramfs as well as legacy ramdisk. 2017-07-06 16:24:30 -07:00
virt KVM: update to new mmu_notifier semantic v2 2017-08-31 16:13:00 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support to generate LLVM assembly files 2017-04-25 08:13:52 +09:00
.mailmap power supply and reset changes for the v4.12 series (part 2) 2017-05-12 12:02:21 -07:00
COPYING
CREDITS avr32: remove support for AVR32 architecture 2017-05-01 09:27:15 +02:00
Kbuild kbuild: Consolidate header generation from ASM offset information 2017-04-13 05:43:37 +09:00
Kconfig
MAINTAINERS Merge branch 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-08-20 09:07:56 -07:00
Makefile Linux 4.13-rc7 2017-08-27 17:20:40 -07:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

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

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

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.