CVE-2026-90176 (GCVE-0-2026-90176)

Vulnerability from cvelistv5 – Published: 2026-09-17 16:07 – Updated: 2026-09-18 17:53
VLAI
Title
ksmbd: Do not skip lock checks for single-byte ranges
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: Do not skip lock checks for single-byte ranges check_lock_range() uses inclusive ranges. Its callers pass the end offset as start + length - 1, so start == end represents a valid single-byte range rather than an empty range. The start == end shortcut therefore skips mandatory byte-range lock checks for one-byte reads, writes, copychunk operations and one-byte truncate ranges. A conflicting lock covering that byte is not checked and the operation is allowed to proceed. Remove the shortcut. The truncate size == inode->i_size case is already handled by only calling check_lock_range() when the new size differs from the current file size.
Severity
8.1 (High)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 52fcbb92e0d3acfd1448b2a43b6595d540da5295 , < a89cc145832e81c32199d4ca2e1ea8bd51ed601d (git)
Affected: da29cd197246c85c0473259f1cad897d9d28faea , < 993e0158331d37c04da18efe551b5e1e35fb3078 (git)
Affected: a6f4cfa3783804336491e0edcb250c25f9b59d33 , < f751d6e39d4c937c45f8fedc66699aa7d2d52288 (git)
Affected: 571204e4758a528fbd67330bd4b0dfbdafb33dd8 , < 84c2d8e807ac489f5c91769293fb15dfdae8bae8 (git)
Affected: 5d510ac31626ed157d2182149559430350cf2104 , < 07a9e289ff7edcc004f58952405f8a65c4e37512 (git)
Affected: 5d510ac31626ed157d2182149559430350cf2104 , < d40c24634fe077a0dc91fd11fccf44ce12b454d5 (git)
Affected: 6.1.160 , < 6.1.188 (semver)
Affected: 6.6.120 , < 6.6.157 (semver)
Affected: 6.12.64 , < 6.12.110 (semver)
Affected: 6.18.3 , < 6.18.52 (semver)
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Linux Linux Affected: 6.19
Unaffected: 0 , < 6.19 (semver)
Unaffected: 6.1.188 , ≤ 6.1.* (semver)
Unaffected: 6.6.157 , ≤ 6.6.* (semver)
Unaffected: 6.12.110 , ≤ 6.12.* (semver)
Unaffected: 6.18.52 , ≤ 6.18.* (semver)
Unaffected: 7.2.6 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
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          "product": "Linux",
          "programFiles": [
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              "version": "7.3-rc1",
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      "cpeApplicability": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: Do not skip lock checks for single-byte ranges\n\ncheck_lock_range() uses inclusive ranges. Its callers pass the end\noffset as start + length - 1, so start == end represents a valid\nsingle-byte range rather than an empty range.\n\nThe start == end shortcut therefore skips mandatory byte-range lock\nchecks for one-byte reads, writes, copychunk operations and one-byte\ntruncate ranges. A conflicting lock covering that byte is not checked\nand the operation is allowed to proceed.\n\nRemove the shortcut. The truncate size == inode-\u003ei_size case is already\nhandled by only calling check_lock_range() when the new size differs\nfrom the current file size."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.1,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The skip is driven by attacker-controlled range length in SMB2 PDUs: smb2_read()/smb2_write() pass Length==1 into ksmbd_vfs_read/write, set_end_of_file_info() passes a 1-byte size change to ksmbd_vfs_truncate(), and FSCTL_SRV_COPYCHUNK Length==1 reaches ksmbd_vfs_copy_file_ranges(); those messages arrive on the ksmbd TCP connection in ksmbd_conn_handler_loop().\nAC:L - Callers pass an inclusive end of start+length-1, so Length==1 makes start==end and the shortcut in check_lock_range() returns 0 before walking ctx-\u003eflc_posix; the attacker sets Length, Offset, EndOfFile, or COPYCHUNK Length in the PDU, and the skip is deterministic with no race or uncontrollable layout.\nPR:L - smb2_check_user_session() requires SMB2_SESSION_VALID before SMB2_READ/WRITE/SET_INFO/IOCTL, smb2_get_ksmbd_tcon() requires a tree connect, and the handlers resolve a fid via ksmbd_lookup_fd_slow(); this is not negotiate or session-setup, so an authenticated SMB share user is required.\nUI:N - The attacker, holding their own session, tree connect, and open handle, sends the one-byte SMB2 READ, WRITE, SET_INFO FILE_END_OF_FILE_INFORMATION, or FSCTL_SRV_COPYCHUNK; no other user must mount media or confirm an action.\nS:U - Bypassing check_lock_range() only allows this ksmbd worker to read or write host file bytes that conflicting FL_POSIX locks on flc_posix should have denied; there is no VM escape, IOMMU bypass, or sandbox boundary crossing.\nC:H - ksmbd_vfs_read() and the COPYCHUNK source check skip exclusive F_WRLCK locks belonging to another filp when start==end, so kernel_read() returns that byte; repeating SMB2 READ at chosen offsets discloses every exclusively locked byte of a file the attacker can open.\nI:H - ksmbd_vfs_write(), ksmbd_vfs_truncate() for size==i_size\u00b11, and COPYCHUNK dest checks likewise skip conflicting F_RDLCK/F_WRLCK, so kernel_write() and vfs_truncate() can overwrite locked bytes or change size by one at attacker-chosen offsets.\nA:N - When the shortcut hits, check_lock_range() returns 0 and the existing kernel_read/kernel_write/vfs_truncate path runs normally; the bug does not NULL-deref, BUG, deadlock, or panic, and the ksmbd worker keeps serving."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-18T17:53:36.125Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/a89cc145832e81c32199d4ca2e1ea8bd51ed601d"
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          "url": "https://git.kernel.org/stable/c/993e0158331d37c04da18efe551b5e1e35fb3078"
        },
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        },
        {
          "url": "https://git.kernel.org/stable/c/d40c24634fe077a0dc91fd11fccf44ce12b454d5"
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      ],
      "title": "ksmbd: Do not skip lock checks for single-byte ranges",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90176",
    "datePublished": "2026-09-17T16:07:02.433Z",
    "dateReserved": "2026-09-11T19:38:34.791Z",
    "dateUpdated": "2026-09-18T17:53:36.125Z",
    "state": "PUBLISHED"
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      "date": "2026-09-25",
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            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: Do not skip lock checks for single-byte ranges\n\ncheck_lock_range() uses inclusive ranges. Its callers pass the end\noffset as start + length - 1, so start == end represents a valid\nsingle-byte range rather than an empty range.\n\nThe start == end shortcut therefore skips mandatory byte-range lock\nchecks for one-byte reads, writes, copychunk operations and one-byte\ntruncate ranges. A conflicting lock covering that byte is not checked\nand the operation is allowed to proceed.\n\nRemove the shortcut. The truncate size == inode-\u003ei_size case is already\nhandled by only calling check_lock_range() when the new size differs\nfrom the current file size."
          }
        ],
        "id": "CVE-2026-90176",
        "lastModified": "2026-09-18T18:17:45.533",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 8.1,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N",
                "version": "3.1"
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              "impactScore": 5.2,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
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        "published": "2026-09-17T17:17:11.387",
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            "url": "https://git.kernel.org/stable/c/a89cc145832e81c32199d4ca2e1ea8bd51ed601d"
          },
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            "url": "https://git.kernel.org/stable/c/f751d6e39d4c937c45f8fedc66699aa7d2d52288"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-21T16:31:34Z",
      "cve": "CVE-2026-90176",
      "id": "CVE-2026-90176",
      "initial_release_date": "2026-09-18T00:20:20Z",
      "product_status:known_not_affected": "347",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-90176",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-90176.json",
      "version": "4"
    }
  }
}



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