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Fencer Vulns
high 7.8

CVE-2024-26759 json

mm/swap: fix race when skipping swapcache

published 2024-04-03 2 y ago modified 2026-08-05 3 mo ago also EUVD-2024-24021

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:

mm/swap: fix race when skipping swapcache

When skipping swapcache for SWP_SYNCHRONOUS_IO, if two or more threads swapin the same entry at the same time, they get different pages (A, B). Before one thread (T0) finishes the swapin and installs page (A) to the PTE, another thread (T1) could finish swapin of page (B), swap_free the entry, then swap out the possibly modified page reusing the same entry. It breaks the pte_same check in (T0) because PTE value is unchanged, causing ABA problem. Thread (T0) will install a stalled page (A) into the PTE and cause data corruption.

One possible callstack is like this:

CPU0 CPU1 ---- ---- do_swap_page() do_swap_page() with same entry <direct swapin path> <direct swapin path> <alloc page A> <alloc page B> swap_read_folio() <- read to page A swap_read_folio() <- read to page B <slow on later locks or interrupt> <finished swapin first> ... set_pte_at() swap_free() <- entry is free <write to page B, now page A stalled> <swap out page B to same swap entry> pte_same() <- Check pass, PTE seems unchanged, but page A is stalled! swap_free() <- page B content lost! set_pte_at() <- staled page A installed!

And besides, for ZRAM, swap_free() allows the swap device to discard the entry content, so even if page (B) is not modified, if swap_read_folio() on CPU0 happens later than swap_free() on CPU1, it may also cause data loss.

To fix this, reuse swapcache_prepare which will pin the swap entry using the cache flag, and allow only one thread to swap it in, also prevent any parallel code from putting the entry in the cache. Release the pin after PT unlocked.

Racers just loop and wait since it's a rare and very short event. A schedule_timeout_uninterruptible(1) call is added to avoid repeated page faults wasting too much CPU, causing livelock or adding too much noise to perf statistics. A similar livelock issue was described in commit 029c4628b2eb ("mm: swap: get rid of livelock in swapin readahead")

Reproducer:

This race issue can be triggered easily using a well constructed reproducer and patched brd (with a delay in read path) [1]:

With latest 6.8 mainline, race caused data loss can be observed easily: $ gcc -g -lpthread test-thread-swap-race.c && ./a.out Polulating 32MB of memory region... Keep swapping out... Starting round 0... Spawning 65536 workers... 32746 workers spawned, wait for done... Round 0: Error on 0x5aa00, expected 32746, got 32743, 3 data loss! Round 0: Error on 0x395200, expected 32746, got 32743, 3 data loss! Round 0: Error on 0x3fd000, expected 32746, got 32737, 9 data loss! Round 0 Failed, 15 data loss!

This reproducer spawns multiple threads sharing the same memory region using a small swap device. Every two threads updates mapped pages one by one in opposite direction trying to create a race, with one dedicated thread keep swapping out the data out using madvise.

The reproducer created a reproduce rate of about once every 5 minutes, so the race should be totally possible in production.

After this patch, I ran the reproducer for over a few hundred rounds and no data loss observed.

Performance overhead is minimal, microbenchmark swapin 10G from 32G zram:

Before: 10934698 us After: 11157121 us Cached: 13155355 us (Dropping SWP_SYNCHRONOUS_IO flag)

[kasong@tencent.com: v4]

Patch / fix

  • Linux Linux 6.1.80, 6.6.19, 6.7.7, 6.8
  • linux Debian 12 6.1.82-1
  • linux Debian 14, Debian 13 6.7.7-1

debian advisories DEBIAN-CVE-2024-26759

  • linux-raspi-realtime Ubuntu Pro Realtime 24.04 LTS 6.8.0-2002.2

ubuntu advisories UBUNTU-CVE-2024-26759

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 9 5.14.0-503.11.1.el9_5
  • rv RHEL 9 5.14.0-503.11.1.el9_5
  • perf RHEL 9 5.14.0-503.11.1.el9_5
  • rtla RHEL 9 5.14.0-503.11.1.el9_5
  • bpftool RHEL 9 7.4.0-503.11.1.el9_5
  • libperf RHEL 9 5.14.0-503.11.1.el9_5
  • kernel-rt RHEL 9 5.14.0-503.11.1.el9_5
  • kernel-64k RHEL 9 5.14.0-503.11.1.el9_5

red hat advisories RHSA-2025:2270RHSA-2024:9315RHSA-2024:4211RHSA-2024:4352

  • kernel-rt Linux Micro 6.0 6.4.0-11.1
  • kernel-source-rt Linux Micro 6.0 6.4.0-11.1
  • kernel-livepatch-MICRO-6-0-RT_Update_3 Linux Micro 6.0 1-1.2
  • kernel-source Linux Micro 6.0 6.4.0-20.1
  • kernel-default Linux Micro 6.0 6.4.0-20.1
  • kernel-kvmsmall Linux Micro 6.0 6.4.0-20.1
  • kernel-default-base Linux Micro 6.0 6.4.0-17.1.1.51
  • kernel-livepatch-MICRO-6-0_Update_3 Linux Micro 6.0 1-1.2

suse advisories SUSE-SU-2025:20077-1SUSE-SU-2025:20073-1SUSE-SU-2024:3592-1SUSE-SU-2024:3587-1SUSE-SU-2024:3569-1SUSE-SU-2024:3564-1

  • 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-2024-26759 updated cvss 5.5

kernel: mm/swap: fix race when skipping swapcache

  • 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: no fix planned “Out of support scope”
  • Red Hat CodeReady Linux Builder (v. 9) libperf 5.14.0-503.11.1.el9_5, kernel-debuginfo-common-s390x 5.14.0-503.11.1.el9_5, kernel-debuginfo-common-x86_64 5.14.0-503.11.1.el9_5, kernel-debuginfo-common-aarch64 5.14.0-503.11.1.el9_5, kernel-debuginfo-common-ppc64le 5.14.0-503.11.1.el9_5
    fixed: vendor fix RHSA-2024:9315
  • Red Hat CodeReady Linux Builder EUS (v.9.4) libperf 5.14.0-427.57.1.el9_4, kernel-debuginfo-common-s390x 5.14.0-427.57.1.el9_4, kernel-debuginfo-common-x86_64 5.14.0-427.57.1.el9_4, kernel-debuginfo-common-aarch64 5.14.0-427.57.1.el9_4, kernel-debuginfo-common-ppc64le 5.14.0-427.57.1.el9_4
    fixed: vendor fix RHSA-2025:2270
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-503.11.1.el9_5, perf 5.14.0-503.11.1.el9_5, rtla 5.14.0-503.11.1.el9_5, kernel-devel-matched 5.14.0-503.11.1.el9_5, kernel-64k-devel-matched 5.14.0-503.11.1.el9_5, kernel-debug-devel-matched 5.14.0-503.11.1.el9_5, +6 more
    fixed: vendor fix RHSA-2024:9315
  • Red Hat Enterprise Linux AppStream EUS (v.9.4) rv 5.14.0-427.57.1.el9_4, perf 5.14.0-427.57.1.el9_4, rtla 5.14.0-427.57.1.el9_4, kernel-devel-matched 5.14.0-427.57.1.el9_4, kernel-64k-devel-matched 5.14.0-427.57.1.el9_4, kernel-debug-devel-matched 5.14.0-427.57.1.el9_4, +6 more
    fixed: vendor fix RHSA-2025:2270
  • 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 RHSA-2024:4211
  • Red Hat Enterprise Linux BaseOS (v. 9) bpftool 7.4.0-503.11.1.el9_5, kernel 5.14.0-503.11.1.el9_5, kernel-64k 5.14.0-503.11.1.el9_5, kernel-core 5.14.0-503.11.1.el9_5, kernel-tools 5.14.0-503.11.1.el9_5, python3-perf 5.14.0-503.11.1.el9_5, +29 more
    fixed: vendor fix RHSA-2024:9315
  • Red Hat Enterprise Linux BaseOS EUS (v.9.4) bpftool 7.3.0-427.57.1.el9_4, kernel 5.14.0-427.57.1.el9_4, kernel-64k 5.14.0-427.57.1.el9_4, kernel-core 5.14.0-427.57.1.el9_4, kernel-tools 5.14.0-427.57.1.el9_4, python3-perf 5.14.0-427.57.1.el9_4, +28 more
    fixed: vendor fix RHSA-2025:2270
show 8 more
  • 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 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
    fixed: vendor fix RHSA-2024:4352
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-503.11.1.el9_5, kernel-rt-core 5.14.0-503.11.1.el9_5, kernel-rt-modules 5.14.0-503.11.1.el9_5, kernel-rt-debug-core 5.14.0-503.11.1.el9_5, kernel-rt-modules-core 5.14.0-503.11.1.el9_5, kernel-rt-debug-modules 5.14.0-503.11.1.el9_5, +4 more
    fixed: vendor fix RHSA-2024:9315
  • Red Hat Enterprise Linux Real Time EUS (v.9.4) kernel-rt 5.14.0-427.57.1.el9_4, kernel-rt-core 5.14.0-427.57.1.el9_4, kernel-rt-modules 5.14.0-427.57.1.el9_4, kernel-rt-debug-core 5.14.0-427.57.1.el9_4, kernel-rt-modules-core 5.14.0-427.57.1.el9_4, kernel-rt-debug-modules 5.14.0-427.57.1.el9_4, +4 more
    fixed: vendor fix RHSA-2025:2270
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-503.11.1.el9_5, kernel-rt-kvm 5.14.0-503.11.1.el9_5, kernel-rt-core 5.14.0-503.11.1.el9_5, kernel-rt-modules 5.14.0-503.11.1.el9_5, kernel-rt-debug-kvm 5.14.0-503.11.1.el9_5, kernel-rt-debug-core 5.14.0-503.11.1.el9_5, +6 more
    fixed: vendor fix RHSA-2024:9315
  • Red Hat Enterprise Linux Real Time for NFV EUS (v.9.4) kernel-rt 5.14.0-427.57.1.el9_4, kernel-rt-kvm 5.14.0-427.57.1.el9_4, kernel-rt-core 5.14.0-427.57.1.el9_4, kernel-rt-modules 5.14.0-427.57.1.el9_4, kernel-rt-debug-kvm 5.14.0-427.57.1.el9_4, kernel-rt-debug-core 5.14.0-427.57.1.el9_4, +6 more
    fixed: vendor fix RHSA-2025:2270
  • 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 RHSA-2024:4352
  • Red Hat CodeReady Linux Builder (v. 9) kernel-cross-headers 5.14.0-503.11.1.el9_5 Red Hat Enterprise Linux AppStream (v. 9) kernel-headers 5.14.0-503.11.1.el9_5 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
    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 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
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.