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Jann Horn a1504a9e20 ipc/sem: Fix dangling sem_array access in semtimedop race 
[ Upstream commit b52be557e2 ]

When __do_semtimedop() goes to sleep because it has to wait for a
semaphore value becoming zero or becoming bigger than some threshold, it
links the on-stack sem_queue to the sem_array, then goes to sleep
without holding a reference on the sem_array.

When __do_semtimedop() comes back out of sleep, one of two things must
happen:

 a) We prove that the on-stack sem_queue has been disconnected from the
    (possibly freed) sem_array, making it safe to return from the stack
    frame that the sem_queue exists in.

 b) We stabilize our reference to the sem_array, lock the sem_array, and
    detach the sem_queue from the sem_array ourselves.

sem_array has RCU lifetime, so for case (b), the reference can be
stabilized inside an RCU read-side critical section by locklessly
checking whether the sem_queue is still connected to the sem_array.

However, the current code does the lockless check on sem_queue before
starting an RCU read-side critical section, so the result of the
lockless check immediately becomes useless.

Fix it by doing rcu_read_lock() before the lockless check.  Now RCU
ensures that if we observe the object being on our queue, the object
can't be freed until rcu_read_unlock().

This bug is only hittable on kernel builds with full preemption support
(either CONFIG_PREEMPT or PREEMPT_DYNAMIC with preempt=full).

Fixes: 370b262c89 ("ipc/sem: avoid idr tree lookup for interrupted semop")
Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2022-12-08 11:18:35 +01:00
Documentation docs: update mediator contact information in CoC doc 2022-11-25 17:40:28 +01:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
arch x86/ioremap: Fix page aligned size calculation in __ioremap_caller() 2022-12-08 11:18:34 +01:00
block block: sed-opal: kmalloc the cmd/resp buffers 2022-11-25 17:40:23 +01:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-25 11:49:16 +02:00
crypto crypto: drbg - make reseeding from get_random_bytes() synchronous 2022-06-25 11:49:13 +02:00
drivers mmc: sdhci: Fix voltage switch delay 2022-12-08 11:18:34 +01:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:21:29 +01:00
fs nilfs2: fix NULL pointer dereference in nilfs_palloc_commit_free_entry() 2022-12-08 11:18:33 +01:00
include mm: Fix '.data.once' orphan section warning 2022-12-08 11:18:34 +01:00
init random: handle latent entropy and command line from random_init() 2022-06-25 11:49:11 +02:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:18:35 +01:00
kernel proc: proc_skip_spaces() shouldn't think it is working on C strings 2022-12-08 11:18:32 +01:00
lib Kconfig.debug: provide a little extra FRAME_WARN leeway when KASAN is enabled 2022-12-08 11:18:34 +01:00
mm v4l2: don't fall back to follow_pfn() if pin_user_pages_fast() fails 2022-12-08 11:18:32 +01:00
net Bluetooth: L2CAP: Fix accepting connection request for invalid SPSM 2022-12-08 11:18:34 +01:00
samples samples/kretprobes: Fix return value if register_kretprobe() failed 2021-11-26 11:36:11 +01:00
scripts scripts/faddr2line: Fix regression in name resolution on ppc64le 2022-12-08 11:18:32 +01:00
security capabilities: fix potential memleak on error path from vfs_getxattr_alloc() 2022-11-10 17:46:55 +01:00
sound ASoC: ops: Fix bounds check for _sx controls 2022-12-08 11:18:34 +01:00
tools tools/vm/slabinfo-gnuplot: use "grep -E" instead of "egrep" 2022-12-08 11:18:33 +01:00
usr initramfs: restore default compression behavior 2020-04-13 10:44:59 +02:00
virt KVM: arm64: vgic: Fix exit condition in scan_its_table() 2022-11-03 23:52:24 +09:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.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 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: co-maintain random.c 2022-06-25 11:49:01 +02:00
Makefile Linux 4.19.267 2022-11-25 17:40:30 +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.