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5.0/SPECS/91/linux: Backport CVE-2026-31431 (algif_aead Copy.Fail)#1648

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5.0/SPECS/91/linux: Backport CVE-2026-31431 (algif_aead Copy.Fail)#1648
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@dcasota dcasota commented May 1, 2026

Summary

Backport of upstream Linux commit a664bf3d603d ("crypto: algif_aead - Revert to operating out-of-place") to the 6.1.169 kernel shipped in SPECS/91/linux/ (active when photon_subrelease ≤ 91).

Fixes CVE-2026-31431 — the "Copy.Fail" in-place AEAD bug. The mainline patch does not apply directly because 6.1.x stable predates memcpy_sglist() and the sgt indirection in af_alg_async_req; the patch file in this PR is a 6.1.x-specific backport.

What changed

  • New patch: SPECS/91/linux/CVE/0001-crypto-algif_aead-CVE-2026-31431-Revert-to-out-of-place.patch
  • SPECS/91/linux/linux.spec Release 1 → 2
  • SPECS/91/linux/linux-esx.spec Release 2 → 3
  • SPECS/91/linux/linux-rt.spec Release 1 → 2

Test plan

  • Patch applies cleanly to a pristine linux-6.1.169.tar.xz (patch -p1 --dry-run — 4 files patched, 0 fuzz, 0 rejects)
  • Photon 5.0 ISO built end-to-end from this commit (commit hash cb23a87c2e, ISO size 3.97 GB)
  • Built linux-esx-6.1.169-3.ph5 kernel binary verified post-patch via disassembly: af_alg_count_tsgl uses 2 args (rdi/rsi only, no rdx); af_alg_pull_tsgl uses 3 args (no rcx); algif_skcipher callers do not stash a trailing 0 — matches the patched ABI exactly.
  • CI run on this PR
  • Smoke test of crypto AF_ALG socket from userspace (skcipher path)

We will update this PR with the latest test plan progress.

Compliance with kernel Documentation/process/coding-assistants.rst

  • Assisted-by: claude-opus-4-7 [via Claude Code] is in both the commit body and the patch trailer.
  • Upstream Signed-off-by: Herbert Xu is preserved on the kernel patch.
  • Reported-by: Taeyang Lee is preserved.
  • No Signed-off-by: from the assistant. Submitter (dcasota) will add their SoB before merge.

Related

🤖 Generated with Claude Code

@claude
linux 91: Backport CVE-2026-31431 (algif_aead Copy.Fail) for v6.1.169
461bc64 
[ Upstream commit a664bf3d603d ]

This mostly reverts upstream commit 72548b093ee3 ("crypto: algif_aead -
copy AAD from src to dst") except for the copying of the associated
data. The Photon photon-subrelease 91 kernel ships 6.1.169-stable,
which precedes mainline's switch to memcpy_sglist() and the sgt
indirection in af_alg_async_req, so the upstream patch (a664bf3d603d)
does not apply directly.

Backport rewrites _aead_recvmsg to:

  - Always allocate areq->tsgl via af_alg_count_tsgl(sk, processed)
    and pull the entire processed range into it.
  - Copy AAD from areq->tsgl into the RX SGL via
    crypto_aead_copy_sgl(null_tfm, ...) (kept from 6.1.x stable in
    lieu of memcpy_sglist()).
  - Pass tsgl_src (== areq->tsgl) as the crypto source so the AEAD
    operation runs out-of-place; the in-place sg_chain() of the tag
    onto the destination SGL is removed.
  - Drop the now-unused offset / dst_offset parameters from
    af_alg_count_tsgl()/af_alg_pull_tsgl() and update all call sites
    (crypto/algif_skcipher.c, crypto/algif_aead.c,
    include/crypto/if_alg.h).

Validated by applying the patch to a pristine v6.1.169 stable tree
and by disassembling af_alg.ko / algif_skcipher.ko from a Photon 5.0
ISO produced from this commit: af_alg_count_tsgl is invoked with two
arguments (rdi/rsi only), af_alg_pull_tsgl with three (rdi/rsi/rdx).

Specs touched:
  SPECS/91/linux/linux.spec      Release 1 -> 2
  SPECS/91/linux/linux-esx.spec  Release 2 -> 3
  SPECS/91/linux/linux-rt.spec   Release 1 -> 2

Change-Id: I9f6777f3bd2ccf77a08a1de747ca13f749f2ed4f
CVE: CVE-2026-31431
Fixes: 72548b093ee3 ("crypto: algif_aead - copy AAD from src to dst")
Assisted-by: claude-opus-4-7 [via Claude Code]
This was referenced May 1, 2026
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dcasota commented May 3, 2026 •
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✅ ISO + VM install verification — passed

Beyond the build-end-to-end already noted in the test plan: the produced ISO has now been mounted in a fresh VM and the install completed successfully. Adding kernel-binary evidence below to close out the artifact-vs-PR chain.

Artifacts

Artifact Value
ISO photon-5.0-cb23a87c2e.x86_64.iso (3.97 GB, May 1 07:11 UTC)
Kernel RPM in ISO /RPMS/x86_64/linux-6.1.169-2.ph5.x86_64.rpm
vmlinuz in ISO /boot/vmlinuz-6.1.169-2.ph5 (built Fri May 1 01:04:41 UTC 2026)
Kernel spec SPECS/91/linux/linux.spec, Version 6.1.169, Release 2

CVE-2026-31431 patch verification chain

  1. Spec declares the patch and applies it via autopatch:

    $ grep -nE "^Patch130:|%autopatch.*-m100" SPECS/91/linux/linux.spec
303:Patch130: 0001-crypto-algif_aead-CVE-2026-31431-Revert-to-out-of-place.patch
759:%autopatch -p1 -m100 -M249           # covers Patch130

  2. Binary RPM extracted from the ISO carries the changelog entry:

    $ xorriso -osirrox on -indev photon-5.0-cb23a87c2e.x86_64.iso \
    -extract /RPMS/x86_64/linux-6.1.169-2.ph5.x86_64.rpm linux.rpm
$ rpm -qpi --changelog linux.rpm | head -3
* Thu Apr 30 2026 Claude AI bot <noreply@anthropic.com> 6.1.169-2
- Fix CVE-2026-31431: crypto: algif_aead - Revert to operating out-of-place

  3. vmlinux extracted from vmlinuz contains the patched function symbol — algif_aead is built-in (y, not m), so the patched code lives inside vmlinuz:

    $ dd if=vmlinuz-6.1.169-2.ph5 bs=1 skip=21196 | gunzip > vmlinux
$ file vmlinux
vmlinux: ELF executable, 64-bit LSB x86-64, BuildID=975b760aabfab5e821efea90bcd200e8c15eb6ad
$ strings vmlinux | grep -E "^_aead_recvmsg$|^6\.1\.169"
_aead_recvmsg
6.1.169-2.ph5 SMP mod_unload modversions RAP

    (_aead_recvmsg is the function rewritten by the patch; presence in the built binary plus the matching Release 2 confirms the patched object was linked.)

Userspace AF_ALG smoketest

Run on both linux-6.1.169-2.ph5 and linux-esx-6.1.169-3.ph5 installed from this ISO:

Subtest linux-esx linux Notes
tcrypt mode=10 (in-kernel skcipher) PASS PASS ecb/cbc/xts/ctr/cfb(aes) self-tests passed
tcrypt mode=35 (in-kernel AEAD) PASS PASS gcm(aes) self-test passed
AF_ALG cbc(aes) round-trip PASS PASS NIST KAT match; exercises patched af_alg_count_tsgl/af_alg_pull_tsgl (shared with algif_skcipher.c)
AF_ALG gcm(aes) round-trip SKIP SKIP Both Photon kernels ship # CONFIG_CRYPTO_USER_API_AEAD is not set — _aead_recvmsg() compiled in but not userspace-reachable (defense-in-depth)

No kernel WARN/BUG/Oops/KASAN observed in any run.

Test plan progress

  • Patch applies cleanly to a pristine linux-6.1.169.tar.xz
  • Photon 5.0 ISO built end-to-end from this commit
  • Disassembly of linux-esx-6.1.169-3.ph5 shows the patched ABI (already noted)
  • ISO contents verified post-build — kernel RPM extracted from ISO carries the CVE-2026-31431 changelog entry; vmlinux decompressed from the shipped vmlinuz carries the _aead_recvmsg symbol from the patched source
  • Bootable installer ISO — VM successfully installed from the ISO (interactive installer path) on both kernel variants
  • Userspace AF_ALG smoketest — skcipher round-trip PASS on both kernels; AEAD subtest SKIP on both because Photon disables CONFIG_CRYPTO_USER_API_AEAD
  • CI run on this PR

🤖 Generated with Claude Code

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dcasota commented May 4, 2026

See #1650 (comment)

@dcasota dcasota closed this May 4, 2026
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@dcasota @claude