Bug 2460713 (CVE-2026-31478)

Summary: CVE-2026-31478 kernel: ksmbd: replace hardcoded hdr2_len with offsetof() in smb2_calc_max_out_buf_len()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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OS: Linux   
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A flaw was found in ksmbd within the Linux kernel. This vulnerability occurs due to an incorrect calculation of the response buffer length in the `smb2_calc_max_out_buf_len()` function. The function used a hardcoded value instead of the proper offset, which could lead to issues in how response buffers are managed.
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Description OSIDB Bzimport 2026-04-22 15:07:00 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ksmbd: replace hardcoded hdr2_len with offsetof() in smb2_calc_max_out_buf_len()

After this commit (e2b76ab8b5c9 "ksmbd: add support for read compound"),
response buffer management was changed to use dynamic iov array.
In the new design, smb2_calc_max_out_buf_len() expects the second
argument (hdr2_len) to be the offset of ->Buffer field in the
response structure, not a hardcoded magic number.
Fix the remaining call sites to use the correct offsetof() value.
Comment 1 Keith Grant 2026-04-22 18:30:52 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042257-CVE-2026-31478-7be0@gregkh/T