UBUNTU-CVE-2026-23249: Medium severity ubuntu/linux-hwe-edge vulnerability
In the Linux kernel, the following vulnerability has been resolved: xfs: check for deleted cursors when revalidating two btrees The free space and inode btree repair functions will rebuild both btrees at the same time, after which it needs to evaluate both btrees to confirm that the corruptions are gone. However, Jiaming Zhang ran syzbot and produced a crash in the second xchkallocbt call. His root-cause analysis is as follows (with minor corrections): In xreprevalidateallocbt(), xchkallocbt() is called twice (first for BNOBT, second for CNTBT). The cause of this issue is that the first call nullified the cursor required by the second call. Let's first enter xreprevalidateallocbt() via following call chain: xfsfileioctl() -> xfsiocscrubvmetadata() -> xfsscrubmetadata() -> sc->ops->repaireval(sc) -> xreprevalidateallocbt() xchkallocbt() is called twice in this function. In the first call: / Note that sc->sm->smtype is XFSSCRUBTYPEBNOPT now / xchkallocbt() -> xchkbtree() -> bs->scrubrec(bs, recp) -> xchkallocbtrec() -> xchkallocbtxref() -> xchkallocbtxrefother() since smtype is XFSSCRUBTYPEBNOBT, pur is set to &sc->sa.cntcur. Kernel called xfsallocgetrec() and returned -EFSCORRUPTED. Call chain: xfsallocgetrec() -> xfsbtreegetrec() -> xfsbtreecheckblock() -> (XFSISCORRUPT || XFSTESTERROR), the former is false and the latter is true, return -EFSCORRUPTED. This should be caused by ioctl$XFSIOCERRORINJECTION I guess. Back to xchkallocbtxrefother(), after receiving -EFSCORRUPTED from xfsallocgetrec(), kernel called xchkshouldcheckxref(). In this function, curpp (points to sc->sa.cntcur) is nullified. Back to xreprevalidateallocbt(), since sc->sa.cntcur has been nullified, it then triggered null-ptr-deref via xchkallocbt() (second call) -> xchkbtree(). So. The bnobt revalidation failed on a cross-reference attempt, so we deleted the cntbt cursor, and then crashed when we tried to revalidate the cntbt. Therefore, check for a null cntbt cursor before that revalidation, and mark the repair incomplete. Also we can ignore the second tree entirely if the first tree was rebuilt but is already corrupt. Apply the same fix to xreprevalidateiallocbt because it has the same problem.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1060.63~22.04.1 - Upgrade
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ubuntu/linux-azure-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1063.71~22.04.1 - Upgrade
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ubuntu/linux-azure-fde-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1062.69~22.04.1 - Upgrade
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ubuntu/linux-gcp-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1063.69~22.04.1 - Upgrade
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ubuntu/linux-hwe-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-136.136~22.04.1 - Upgrade
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ubuntu/linux-ibm-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1060.61~22.04.1 - Upgrade
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ubuntu/linux-lowlatency-hwe-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-134.134.1~22.04.1 - Upgrade
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ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1060.63+fips1 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1062.69+fips1 - Upgrade
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ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-134.134+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1063.69+fips1 - Compensating control
In xrep_revalidate_allocbt(), check whether the cntbt cursor is null before the second xchk_allocbt() revalidation; if the first-tree revalidation failed and deleted the cursor, skip revalidating the second tree and mark the repair incomplete. Apply the same fix to xrep_revalidate_iallocbt().
Event History
Frequently Asked Questions
What access does an attacker need?
Exploitation requires local access and low privileges. No user interaction is required.
What is the likely security impact?
The published vector indicates a high availability impact, with no confidentiality or integrity impact. The described failure is a kernel crash during XFS btree repair revalidation.
Which Ubuntu kernel packages are identified as affected?
The listed packages are ubuntu/linux-riscv, ubuntu/linux-realtime, ubuntu/linux-azure, ubuntu/linux-gcp, ubuntu/linux-azure-fde, ubuntu/linux-hwe-edge, ubuntu/linux-gke, and ubuntu/linux-gkeop.