Bug 2536251 (CVE-2026-90176)

Summary: CVE-2026-90176 kernel: ksmbd: Do not skip lock checks for single-byte ranges
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in ksmbd, a server message block (SMB) protocol implementation within the Linux kernel. A logic error in the check_lock_range() function, which is responsible for enforcing file locks, causes it to bypass mandatory byte-range lock checks for single-byte operations. This allows an attacker to perform read, write, or truncate operations on a single byte within a file, even if that byte is protected by a conflicting lock. This could lead to unauthorized modification or access to data, potentially compromising data integrity.
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Description OSIDB Bzimport 2026-09-17 17:07:31 UTC 
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.
Comment 1 Keith Grant 2026-09-23 20:29:13 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-90176.mbox