CVE-2021-47640 json
powerpc/kasan: Fix early region not updated correctly
published 2025-02-26 20 mo ago modified 2026-06-17 4 mo ago also EUVD-2021-34664
- 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 17%
- public exploits
- 0
- none known
Summary
In the Linux kernel, the following vulnerability has been resolved:
powerpc/kasan: Fix early region not updated correctly
The shadow's page table is not updated when PTE_RPN_SHIFT is 24 and PAGE_SHIFT is 12. It not only causes false positives but also false negative as shown the following text.
Fix it by bringing the logic of kasan_early_shadow_page_entry here.
1. False Positive: ================================================================== BUG: KASAN: vmalloc-out-of-bounds in pcpu_alloc+0x508/0xa50 Write of size 16 at addr f57f3be0 by task swapper/0/1
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.15.0-12267-gdebe436e77c7 #1 Call Trace: [c80d1c20] [c07fe7b8] dump_stack_lvl+0x4c/0x6c (unreliable) [c80d1c40] [c02ff668] print_address_description.constprop.0+0x88/0x300 [c80d1c70] [c02ff45c] kasan_report+0x1ec/0x200 [c80d1cb0] [c0300b20] kasan_check_range+0x160/0x2f0 [c80d1cc0] [c03018a4] memset+0x34/0x90 [c80d1ce0] [c0280108] pcpu_alloc+0x508/0xa50 [c80d1d40] [c02fd7bc] __kmem_cache_create+0xfc/0x570 [c80d1d70] [c0283d64] kmem_cache_create_usercopy+0x274/0x3e0 [c80d1db0] [c2036580] init_sd+0xc4/0x1d0 [c80d1de0] [c00044a0] do_one_initcall+0xc0/0x33c [c80d1eb0] [c2001624] kernel_init_freeable+0x2c8/0x384 [c80d1ef0] [c0004b14] kernel_init+0x24/0x170 [c80d1f10] [c001b26c] ret_from_kernel_thread+0x5c/0x64
Memory state around the buggy address: f57f3a80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f57f3b00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 >f57f3b80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ^ f57f3c00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f57f3c80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ==================================================================
2. False Negative (with KASAN tests): ================================================================== Before fix: ok 45 - kmalloc_double_kzfree # vmalloc_oob: EXPECTATION FAILED at lib/test_kasan.c:1039 KASAN failure expected in "((volatile char *)area)[3100]", but none occurred not ok 46 - vmalloc_oob not ok 1 - kasan
================================================================== After fix: ok 1 - kasan
Patch / fix
- Linux Linux 5.4, 5.4.189, 5.10.110, 5.15.33, 5.16.19, 5.17.2, 5.18
- linux Debian 14, Debian 13, Debian 12 5.17.3-1
debian advisories DEBIAN-CVE-2021-47640
- linux Ubuntu 20.04 LTS 5.4.0-117.132
- linux Ubuntu 22.04 LTS 5.15.0-37.39
- linux-aws Ubuntu 20.04 LTS 5.4.0-1078.84
- linux-aws Ubuntu 22.04 LTS 5.15.0-1011.14
- linux-gcp Ubuntu 20.04 LTS 5.4.0-1078.84
- linux-gcp Ubuntu 22.04 LTS 5.15.0-1008.12
- linux-gke Ubuntu 22.04 LTS 5.15.0-1008.10
- linux-ibm Ubuntu 20.04 LTS 5.4.0-1026.29
ubuntu advisories UBUNTU-CVE-2021-47640
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
- git.kernel.org/stable/c/7f19245c3647afea8c7c41f795506ef70f64b9f2 commit
- git.kernel.org/stable/c/f39a3309393a4a484532f6ba745c6acbcfe06115 commit
- git.kernel.org/stable/c/5a3d8f3192a409893c57808cc935e16484df1068 commit
- git.kernel.org/stable/c/de56beace6648065d404cd9835aa7d30e3df519d commit
- git.kernel.org/stable/c/e3d157a4b4f4e0268c98be5b7013bf4b31234bb6 commit
- git.kernel.org/stable/c/dd75080aa8409ce10d50fb58981c6b59bf8707d3 commit
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-2021-47640 updated cvss 7.8
kernel: powerpc/kasan: Fix early region not updated correctly
-
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 Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernelnot 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
- total
- Assessed
- 13 mo ago
Exploit prediction
0.26% chance of exploitation in the next 30 days, higher than 17% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CISA ADP | 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 | 7.8 | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H |
| CNA | 3.1 | 7.8 | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H |
Affected products
- Linux Linux
Classification
- Weakness
-
- CWE-787 Out-of-bounds Write
- Technology feeds
References
-
git.kernel.org
/stable/c/7f19245c3647afea8c7c41f795506ef70f64b9f2
patch
-
git.kernel.org
/stable/c/f39a3309393a4a484532f6ba745c6acbcfe06115
patch
-
git.kernel.org
/stable/c/5a3d8f3192a409893c57808cc935e16484df1068
patch
-
git.kernel.org
/stable/c/de56beace6648065d404cd9835aa7d30e3df519d
patch
-
git.kernel.org
/stable/c/e3d157a4b4f4e0268c98be5b7013bf4b31234bb6
patch
-
git.kernel.org
/stable/c/dd75080aa8409ce10d50fb58981c6b59bf8707d3
patch
Sources
- CVE List CVE-2021-47640
- NVD CVE-2021-47640
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