CVE-2021-47640

HIGH EPSS 14.9%
Published Feb 26, 20251y ago · Modified Jun 17, 20262w ago
7.8 CVSS 3.1
High
Find Similar
Published Feb 26, 2025 1y ago
Last Modified Jun 17, 2026 2w ago

Description

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

CVSS Details

Base Score
7.8
Exploitability
1.8
Impact
5.9
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Attack Vector Local
Attack Complexity Low
Privileges Required Low
User Interaction None
Scope Unchanged
Confidentiality High
Integrity High
Availability High

Threat Intelligence

EPSS Exploit Probability
14.9% percentile
Exploit & Patch Status
No Known Exploit
Patch Available

Weaknesses 1

CWE-787 Out-of-bounds Write Memory Safety

Affected Products 5

VendorProductVersionRange
linuxlinux_kernel*≥5.4  –  <5.4.189
linuxlinux_kernel*≥5.5  –  <5.10.110
linuxlinux_kernel*≥5.11  –  <5.15.33
linuxlinux_kernel*≥5.16  –  <5.16.19
linuxlinux_kernel*≥5.17  –  <5.17.2

References 6

  • git.kernel.org https://git.kernel.org/stable/c/5a3d8f3192a409893c57808cc935e16484df1068
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/7f19245c3647afea8c7c41f795506ef70f64b9f2
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/dd75080aa8409ce10d50fb58981c6b59bf8707d3
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/de56beace6648065d404cd9835aa7d30e3df519d
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/e3d157a4b4f4e0268c98be5b7013bf4b31234bb6
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/f39a3309393a4a484532f6ba745c6acbcfe06115
    Patch

Remediation

  • git.kernel.org https://git.kernel.org/stable/c/5a3d8f3192a409893c57808cc935e16484df1068
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/7f19245c3647afea8c7c41f795506ef70f64b9f2
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/dd75080aa8409ce10d50fb58981c6b59bf8707d3
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/de56beace6648065d404cd9835aa7d30e3df519d
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/e3d157a4b4f4e0268c98be5b7013bf4b31234bb6
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/f39a3309393a4a484532f6ba745c6acbcfe06115
    Patch