UBUNTU-CVE-2026-74359: Use After Free
In the Linux kernel, the following vulnerability has been resolved: configfslookup(): don't leave ->sdentry dangling on failure Normally ->sdentry is cleared when dentry it's pointing to becomes negative (on eviction, realistically). However, that only happens if dentry gets to be positive in the first place; in case of inode allocation failure dentry never becomes positive, so ->diput() is not called at all. We do part of what normally would've been done by configfsdiput() (dropping the reference to configfsdirent) manually, but we do not clear ->sdentry there. Sloppy as it is, it does not matter in case of configfscreate{dir,link}() - there configfsdirent does not survive dropping the sole reference to it. However, for configfslookup() it does survive, with a dangling pointer to soon to be freed dentry sitting it its ->sdentry. Subsequent getdents(2) in that directory will end up dereferencing that pointer in order to pick the inode number. Use after free... This is the minimal fix; the right approach is to set the linkage between dentry and configfsdirent only after we know that we have an inode, but that takes more surgery and the bug had been there since 2006, so...
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 6.8.1-1062.63 - Upgrade
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ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1067.70+fips1 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79+fips1 - Upgrade
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ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-147.147+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79+fips1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-38.38 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 7.0.0-1016.16 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1
Event History
Frequently Asked Questions
Who is realistically exposed to this issue?
Systems running the listed Ubuntu kernel packages are potentially exposed when configfs is used and a configfs directory lookup encounters an inode allocation failure. The vulnerable path involves a surviving configfs_dirent with a dangling s_dentry pointer.
What conditions are needed to trigger the use-after-free?
An inode allocation failure during configfs_lookup() must occur after the configfs_dirent has been linked to the dentry. A subsequent getdents(2) call on the affected directory dereferences the dangling pointer while obtaining an inode number.
Is normal configfs directory or link creation affected in the same way?
The description states that configfs_create_dir() and configfs_create_link() do not have the same practical impact, because their configfs_dirent does not survive after its sole reference is dropped. The problematic surviving object is associated with configfs_lookup().
How can an affected condition be identified?
The relevant condition is a configfs lookup failure caused by inode allocation failure, followed by getdents(2) on that directory. The provided information does not describe a log signature, detection command, or other external indicator.