Bug 2422655 (CVE-2025-40363)

Summary: CVE-2025-40363 kernel: net: ipv6: fix field-spanning memcpy warning in AH output
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: unspecifiedKeywords: Security
Target Milestone: ---   
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2025-12-16 14:01:15 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net: ipv6: fix field-spanning memcpy warning in AH output

Fix field-spanning memcpy warnings in ah6_output() and
ah6_output_done() where extension headers are copied to/from IPv6
address fields, triggering fortify-string warnings about writes beyond
the 16-byte address fields.

  memcpy: detected field-spanning write (size 40) of single field "&top_iph->saddr" at net/ipv6/ah6.c:439 (size 16)
  WARNING: CPU: 0 PID: 8838 at net/ipv6/ah6.c:439 ah6_output+0xe7e/0x14e0 net/ipv6/ah6.c:439

The warnings are false positives as the extension headers are
intentionally placed after the IPv6 header in memory. Fix by properly
copying addresses and extension headers separately, and introduce
helper functions to avoid code duplication.
Comment 1 Alexander B 2025-12-17 05:39:10 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025121645-CVE-2025-40363-bbdd@gregkh/T