Bug 2513300 (CVE-2026-68385)

Summary: CVE-2026-68385 kernel: s390/checksum: Fix csum_partial() without vector facility
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's s390 architecture checksumming mechanism. On systems without a vector facility, the csum_partial() function incorrectly calculates checksums. This occurs because the csum_copy() function, when called with specific parameters, falls back to calculating the checksum from memory address zero instead of the intended source buffer. This can lead to incorrect checksums, potentially affecting data integrity within the kernel.
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Description OSIDB Bzimport 2026-08-10 12:29:41 UTC 
In the Linux kernel, the following vulnerability has been resolved:

s390/checksum: Fix csum_partial() without vector facility

Currently csum_partial() calls csum_copy() with copy=false and dst=NULL.
On machines without the vector facility, csum_copy() falls back to
cksm(dst, ...), causing the checksum to be calculated from address zero
instead of the source buffer.

The VX implementation already checksums data loaded from src. Make the
fallback do the same by passing src to cksm().