{ "schema_version": "1.6.1", "id": "RPI-CVE-2026-90176", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2026-90176" ], "published": "2026-09-17T16:10:40Z", "summary": "ksmbd: Do not skip lock checks for single-byte ranges", "details": "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->i_size case is already\nhandled by only calling check_lock_range() when the new size differs\nfrom the current file size.", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.12.75-1+rpt1~bookworm", "1:6.12.87-1+rpt1~bookworm", "1:6.12.93-1+rpt1", "1:6.12.96-1+rpt1", "1:6.12.109-1+rpt1" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.12.75+rpt-rpi-2712", "binary_version": "1:6.12.75-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.75+rpt-rpi-v6", "binary_version": "1:6.12.75-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.75+rpt-rpi-v7", "binary_version": "1:6.12.75-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.75+rpt-rpi-v7l", "binary_version": "1:6.12.75-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.75+rpt-rpi-v8", "binary_version": 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"upstream_version": "6.18.33", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.18.52" }, "1:6.18.34-1+rpt1": { "linux_commit": "c8c7494100e99ee05b11aaa4f0588a223a63d1af", "upstream_version": "6.18.34", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.18.52" }, "1:6.18.39-1+rpt1": { "linux_commit": "60ea684a8ace97bb0db1a16e20753bdd6ab371ff", "upstream_version": "6.18.39", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.18.52" }, "1:6.18.50-1+rpt1": { "linux_commit": "cff533aec2fa601846766b32ff57204e0a61bed7", "upstream_version": "6.18.50", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.18.52" } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2026-90176" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/a89cc145832e81c32199d4ca2e1ea8bd51ed601d" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/993e0158331d37c04da18efe551b5e1e35fb3078" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/f751d6e39d4c937c45f8fedc66699aa7d2d52288" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/84c2d8e807ac489f5c91769293fb15dfdae8bae8" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/07a9e289ff7edcc004f58952405f8a65c4e37512" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/d40c24634fe077a0dc91fd11fccf44ce12b454d5" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-09-18T17:55:42Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 8.1, "cvss_v3_severity": "High", "scenario": "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->flc_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." } } }