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CVE-2026-45942— ext4: fix e4b bitmap inconsistency reports

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于ext4文件系统中页面迁移与位图修改之间的竞争条件，可能导致e4b位图不一致报告。

CVSS 7.8 · High EPSS 0.10% · P1

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 12

VendorProduct Version RangeStatus
Linux Linux c9de560ded61faa5b754137b7753da252391c55a< 57e83bfbe1e412ac42daced2086f3c6f9a17bba0 affected
c9de560ded61faa5b754137b7753da252391c55a< c05033cfc5c7699cd4df8d48cef94d01da755f24 affected
c9de560ded61faa5b754137b7753da252391c55a< 29a07d691d282faf38c33d4b61839b89399110f9 affected
c9de560ded61faa5b754137b7753da252391c55a< f29709a7a3fc38f5015d850504762cdef0e151f9 affected
c9de560ded61faa5b754137b7753da252391c55a< bdc56a9c46b2a99c12313122b9352b619a2e719e affected
2.6.25 affected
< 2.6.25 unaffected
6.6.130≤ 6.6.* unaffected
… +4 more rows
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I. Basic Information for CVE-2026-45942

Vulnerability Information
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Vulnerability Title
ext4: fix e4b bitmap inconsistency reports
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: ext4: fix e4b bitmap inconsistency reports A bitmap inconsistency issue was observed during stress tests under mixed huge-page workloads. Ext4 reported multiple e4b bitmap check failures like: ext4_mb_complex_scan_group:2508: group 350, 8179 free clusters as per group info. But got 8192 blocks Analysis and experimentation confirmed that the issue is caused by a race condition between page migration and bitmap modification. Although this timing window is extremely narrow, it is still hit in practice: folio_lock ext4_mb_load_buddy __migrate_folio check ref count folio_mc_copy __filemap_get_folio folio_try_get(folio) ...... mb_mark_used ext4_mb_unload_buddy __folio_migrate_mapping folio_ref_freeze folio_unlock The root cause of this issue is that the fast path of load_buddy only increments the folio's reference count, which is insufficient to prevent concurrent folio migration. We observed that the folio migration process acquires the folio lock. Therefore, we can determine whether to take the fast path in load_buddy by checking the lock status. If the folio is locked, we opt for the slow path (which acquires the lock) to close this concurrency window. Additionally, this change addresses the following issues: When the DOUBLE_CHECK macro is enabled to inspect bitmap-related issues, the following error may be triggered: corruption in group 324 at byte 784(6272): f in copy != ff on disk/prealloc Analysis reveals that this is a false positive. There is a specific race window where the bitmap and the group descriptor become momentarily inconsistent, leading to this error report: ext4_mb_load_buddy ext4_mb_load_buddy __filemap_get_folio(create|lock) folio_lock ext4_mb_init_cache folio_mark_uptodate __filemap_get_folio(no lock) ...... mb_mark_used mb_mark_used_double mb_cmp_bitmaps mb_set_bits(e4b->bd_bitmap) folio_unlock The original logic assumed that since mb_cmp_bitmaps is called when the bitmap is newly loaded from disk, the folio lock would be sufficient to prevent concurrent access. However, this overlooks a specific race condition: if another process attempts to load buddy and finds the folio is already in an uptodate state, it will immediately begin using it without holding folio lock.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于ext4文件系统中页面迁移与位图修改之间的竞争条件，可能导致e4b位图不一致报告。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux c9de560ded61faa5b754137b7753da252391c55a ~ 57e83bfbe1e412ac42daced2086f3c6f9a17bba0 -
Linux Linux 2.6.25 -

II. Public POCs for CVE-2026-45942

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III. Intelligence Information for CVE-2026-45942

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Patches & Fixes for CVE-2026-45942 (4)

Same Patch Batch · Linux · 2026-05-27 · 275 CVEs total

CVE-2026-45898 9.8 CRITICAL RDMA/iwcm: Fix workqueue list corruption by removing work_list
CVE-2026-46039 9.8 CRITICAL rxgk: Fix potential integer overflow in length check
CVE-2026-45988 9.8 CRITICAL rxrpc: Fix re-decryption of RESPONSE packets
CVE-2026-45972 9.8 CRITICAL smb: client: fix potential UAF and double free in smb2_open_file()
CVE-2026-46043 9.1 CRITICAL RDMA/rxe: Validate pad and ICRC before payload_size() in rxe_rcv
CVE-2026-45945 8.8 HIGH iommu/vt-d: Fix race condition during PASID entry replacement
CVE-2026-46056 8.8 HIGH Bluetooth: hci_event: fix potential UAF in SSP passkey handlers
CVE-2026-45843 8.2 HIGH slip: bound decode() reads against the compressed packet length
CVE-2026-46037 8.2 HIGH ipv4: icmp: validate reply type before using icmp_pointers
CVE-2025-71311 8.2 HIGH fs/ntfs3: Initialize new folios before use
CVE-2026-46010 8.1 HIGH rxrpc: Fix error handling in rxgk_extract_token()
CVE-2026-46099 8.1 HIGH net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels
CVE-2026-46076 7.9 HIGH KVM: nSVM: Raise #UD if unhandled VMMCALL isn't intercepted by L1
CVE-2026-45931 7.8 HIGH accel/amdxdna: Hold mm structure across iommu_sva_unbind_device()
CVE-2026-45951 7.8 HIGH bpf: Fix a potential use-after-free of BTF object
CVE-2026-45935 7.8 HIGH fs/ntfs3: Fix slab-out-of-bounds read in DeleteIndexEntryRoot
CVE-2026-45933 7.8 HIGH bpf: Preserve id of register in sync_linked_regs()
CVE-2026-45984 7.8 HIGH gfs2: Fix use-after-free in iomap inline data write path
CVE-2026-45862 7.8 HIGH iommu/vt-d: Flush cache for PASID table before using it
CVE-2026-45861 7.8 HIGH gfs2: Fix slab-use-after-free in qd_put

Showing top 20 of 275 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-45942

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