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CVE-2026-72225: jbd2: fix integer underflow in jbd2_journal_initialize_fast_commit()

• Severity: high (CVSS 7.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-15 · updated 2026-10-16

Description

In the Linux kernel, the following vulnerability has been resolved: jbd2: fix integer underflow in jbd2_journal_initialize_fast_commit() jbd2_journal_initialize_fast_commit() validates journal capacity by checking (journal->j_last - num_fc_blks < JBD2_MIN_JOURNAL_BLOCKS). Both j_last and num_fc_blks are unsigned, so when num_fc_blks exceeds j_last the subtraction wraps to a large value, bypassing the bounds check. The resulting underflow corrupts j_last, j_fc_first, and j_free, leading to journal abort. Fix by checking num_fc_blks against j_last before the subtraction, returning -EFSCORRUPTED.

Affected products

• Linux kernel: 5.10 — fixed in 7.2

How to fix

Upgrade to a fixed version: Linux kernel 7.2. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/289a2ca0c9b7eae74f93fc213b0b971669b8683d
• https://git.kernel.org/stable/c/4450dcaadf7d4aae8b6e4223b5d6ee4eb77097a9
• https://git.kernel.org/stable/c/4b48dcb88bb9117e3d3f051175a9a8b7cff7f8b6
• https://git.kernel.org/stable/c/78955fdce8ff654e6d33a2fa90882a1e7eb26330
• https://git.kernel.org/stable/c/a58fc10adf503969fec2007b5afe8987258046c4
• https://git.kernel.org/stable/c/aa90f00932bf572d6ef284c977c2a60b39c13bd6
• https://git.kernel.org/stable/c/e144ad0250f77e23e28949587b8b57e40dc3b512
• https://git.kernel.org/stable/c/fb9b49618ed7296ebfad62a3835da8945f727001

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