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Fencer Vulns
high 7.8

CVE-2021-47069 json

ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry

published 2024-03-01 2 y ago modified 2026-08-05 3 mo ago also EUVD-2021-33717

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 18%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry

do_mq_timedreceive calls wq_sleep with a stack local address. The sender (do_mq_timedsend) uses this address to later call pipelined_send.

This leads to a very hard to trigger race where a do_mq_timedreceive call might return and leave do_mq_timedsend to rely on an invalid address, causing the following crash:

RIP: 0010:wake_q_add_safe+0x13/0x60 Call Trace: __x64_sys_mq_timedsend+0x2a9/0x490 do_syscall_64+0x80/0x680 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x7f5928e40343

The race occurs as:

1. do_mq_timedreceive calls wq_sleep with the address of `struct ext_wait_queue` on function stack (aliased as `ewq_addr` here) - it holds a valid `struct ext_wait_queue *` as long as the stack has not been overwritten.

2. `ewq_addr` gets added to info->e_wait_q[RECV].list in wq_add, and do_mq_timedsend receives it via wq_get_first_waiter(info, RECV) to call __pipelined_op.

3. Sender calls __pipelined_op::smp_store_release(&this->state, STATE_READY). Here is where the race window begins. (`this` is `ewq_addr`.)

4. If the receiver wakes up now in do_mq_timedreceive::wq_sleep, it will see `state == STATE_READY` and break.

5. do_mq_timedreceive returns, and `ewq_addr` is no longer guaranteed to be a `struct ext_wait_queue *` since it was on do_mq_timedreceive's stack. (Although the address may not get overwritten until another function happens to touch it, which means it can persist around for an indefinite time.)

6. do_mq_timedsend::__pipelined_op() still believes `ewq_addr` is a `struct ext_wait_queue *`, and uses it to find a task_struct to pass to the wake_q_add_safe call. In the lucky case where nothing has overwritten `ewq_addr` yet, `ewq_addr->task` is the right task_struct. In the unlucky case, __pipelined_op::wake_q_add_safe gets handed a bogus address as the receiver's task_struct causing the crash.

do_mq_timedsend::__pipelined_op() should not dereference `this` after setting STATE_READY, as the receiver counterpart is now free to return. Change __pipelined_op to call wake_q_add_safe on the receiver's task_struct returned by get_task_struct, instead of dereferencing `this` which sits on the receiver's stack.

As Manfred pointed out, the race potentially also exists in ipc/msg.c::expunge_all and ipc/sem.c::wake_up_sem_queue_prepare. Fix those in the same way.

Patch / fix

  • Linux Linux 5.10.40, 5.12.7, 5.13
  • linux Debian 14, Debian 13, Debian 12 5.10.40-1

debian advisories DEBIAN-CVE-2021-47069

  • kernel RHEL 8 4.18.0-553.8.1.el8_10
  • perf RHEL 8 4.18.0-553.8.1.el8_10
  • bpftool RHEL 8 4.18.0-553.8.1.el8_10
  • kernel-core RHEL 8 4.18.0-553.8.1.el8_10
  • kernel-tools RHEL 8 4.18.0-553.8.1.el8_10
  • python3-perf RHEL 8 4.18.0-553.8.1.el8_10
  • kernel-modules RHEL 8 4.18.0-553.8.1.el8_10
  • kernel-zfcpdump RHEL 8 4.18.0-553.8.1.el8_10

red hat advisories RHSA-2024:6206RHSA-2024:4211RHSA-2024:5692RHSA-2024:4352

  • kernel-64kb SLES 15 SP3-LTSS, SLE High Performance Computing 15 SP3-LTSS, Enterprise Storage 7.1 5.3.18-150300.59.179.1
  • kernel-syms SLES for SAP 15 SP3, SLES 15 SP3-LTSS, SLE High Performance Computing 15 SP3-LTSS +1 more 5.3.18-150300.59.179.1
  • kernel-source SLES for SAP 15 SP3, SLES 15 SP3-LTSS, SLE High Performance Computing 15 SP3-LTSS +1 more 5.3.18-150300.59.179.1
  • kernel-default SLES for SAP 15 SP3, SLES 15 SP3-LTSS, SLE Micro 5.2 +5 more 5.3.18-150300.59.179.1
  • kernel-preempt SLES for SAP 15 SP3, SLES 15 SP3-LTSS, SLE High Performance Computing 15 SP3-LTSS +1 more 5.3.18-150300.59.179.1
  • kernel-obs-build SLES for SAP 15 SP3, SLES 15 SP3-LTSS, SLE High Performance Computing 15 SP3-LTSS +1 more 5.3.18-150300.59.179.1
  • kernel-default-base SLES for SAP 15 SP3, SLES 15 SP3-LTSS, SLE Micro 5.2 +3 more 5.3.18-150300.59.179.1.150300.18.105.2
  • kernel-default SLES for SAP 15 SP2, SLES 15 SP2-LTSS, SLE Live Patching 15 SP2 +2 more 5.3.18-150200.24.206.1

suse advisories SUSE-SU-2024:3585-1SUSE-SU-2024:3565-1SUSE-SU-2024:1489-1SUSE-SU-2024:1454-1SUSE-SU-2024:0926-1SUSE-SU-2024:0857-1

  • kernel-rt AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-kvm AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-core AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-modules AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-debug-kvm AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-debug-core AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-debug-modules AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel-rt-modules-extra AlmaLinux 8 4.18.0-553.8.1.rt7.349.el8_10

almalinux advisories ALSA-2024:4352ALSA-2024:4211

  • kernel-rt Rocky Linux 8 4.18.0-553.8.1.rt7.349.el8_10
  • kernel Rocky Linux 8 4.18.0-553.8.1.el8_10

rocky linux advisories RLSA-2024:4352RLSA-2024:4211

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-47069 updated cvss 5.8

kernel: ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: workaround, no fix planned “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.”
  • Red Hat CodeReady Linux Builder EUS (v.8.8) kernel-debuginfo-common-x86_64 4.18.0-477.70.1.el8_8, kernel-debuginfo-common-aarch64 4.18.0-477.70.1.el8_8, kernel-debuginfo-common-ppc64le 4.18.0-477.70.1.el8_8
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2024:6206
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.8.1.el8_10, kernel 4.18.0-553.8.1.el8_10, bpftool 4.18.0-553.8.1.el8_10, kernel-core 4.18.0-553.8.1.el8_10, kernel-tools 4.18.0-553.8.1.el8_10, python3-perf 4.18.0-553.8.1.el8_10, +15 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2024:4211
  • Red Hat Enterprise Linux BaseOS AUS (v.8.6) perf 4.18.0-372.119.1.el8_6, kernel 4.18.0-372.119.1.el8_6, bpftool 4.18.0-372.119.1.el8_6, kernel-core 4.18.0-372.119.1.el8_6, kernel-tools 4.18.0-372.119.1.el8_6, python3-perf 4.18.0-372.119.1.el8_6, +8 more Red Hat Enterprise Linux BaseOS E4S (v.8.6) perf 4.18.0-372.119.1.el8_6, kernel 4.18.0-372.119.1.el8_6, bpftool 4.18.0-372.119.1.el8_6, kernel-core 4.18.0-372.119.1.el8_6, kernel-tools 4.18.0-372.119.1.el8_6, python3-perf 4.18.0-372.119.1.el8_6, +15 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2024:5692
  • Red Hat Enterprise Linux BaseOS EUS (v.8.8) perf 4.18.0-477.70.1.el8_8, kernel 4.18.0-477.70.1.el8_8, bpftool 4.18.0-477.70.1.el8_8, kernel-core 4.18.0-477.70.1.el8_8, kernel-tools 4.18.0-477.70.1.el8_8, python3-perf 4.18.0-477.70.1.el8_8, +15 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2024:6206
  • Red Hat Enterprise Linux BaseOS TUS (v.8.6) perf 4.18.0-372.119.1.el8_6, kernel 4.18.0-372.119.1.el8_6, bpftool 4.18.0-372.119.1.el8_6, kernel-core 4.18.0-372.119.1.el8_6, kernel-tools 4.18.0-372.119.1.el8_6, python3-perf 4.18.0-372.119.1.el8_6, +8 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2024:5692
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.8.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.8.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.8.1.el8_10
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2024:4211
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-kvm 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-core 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-modules 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-debug-kvm 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-debug-core 4.18.0-553.8.1.rt7.349.el8_10, +4 more Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-core 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-modules 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-debug-core 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-debug-modules 4.18.0-553.8.1.rt7.349.el8_10, kernel-rt-modules-extra 4.18.0-553.8.1.rt7.349.el8_10, +2 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2024:4352
show 1 more
  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux BaseOS (v. 8) kernel-headers 4.18.0-553.8.1.el8_10, kernel-cross-headers 4.18.0-553.8.1.el8_10 Red Hat Enterprise Linux BaseOS AUS (v.8.6) kernel-doc 4.18.0-372.119.1.el8_6 Red Hat Enterprise Linux BaseOS E4S (v.8.6) kernel-doc 4.18.0-372.119.1.el8_6 Red Hat Enterprise Linux BaseOS TUS (v.8.6) kernel-doc 4.18.0-372.119.1.el8_6
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.26% chance of exploitation in the next 30 days, higher than 18% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 7.0 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Linux Linux

Classification

Weakness
  • CWE-672 Operation on a Resource after Expiration or Release
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.