jbd2: fix integer underflow in jbd2_journal_initialize_fast_commit()

Summary

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.

Timeline

1. Aug 15, 2026, 5:54 AM UTCCVE published
2. Oct 16, 2026, 6:44 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Oct 16, 2026, 6:45 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 6866d7b3f2bb4f011041ba54c98b1584497fe2fd · fixed in aa90f00932bf572d6ef284c977c2a60b39c13bd6; From 6866d7b3f2bb4f011041ba54c98b1584497fe2fd · fixed in e144ad0250f77e23e28949587b8b57e40dc3b512; From 6866d7b3f2bb4f011041ba54c98b1584497fe2fd · fixed in 4b48dcb88bb9117e3d3f051175a9a8b7cff7f8b6; From 6866d7b3f2bb4f011041ba54c98b1584497fe2fd · fixed in fb9b49618ed7296ebfad62a3835da8945f727001; From 6866d7b3f2bb4f011041ba54c98b1584497fe2fd · fixed in 4450dcaadf7d4aae8b6e4223b5d6ee4eb77097a9; From 6866d7b3f2bb4f011041ba54c98b1584497fe2fd · fixed in 78955fdce8ff654e6d33a2fa90882a1e7eb26330; From 6866d7b3f2bb4f011041ba54c98b1584497fe2fd · fixed in a58fc10adf503969fec2007b5afe8987258046c4; From 6866d7b3f2bb4f011041ba54c98b1584497fe2fd · fixed in 289a2ca0c9b7eae74f93fc213b0b971669b8683d

• Linux Linux

  5.10

• KernelLinux

  From 5.10.0 · fixed in 5.10.266; From 5.11.0 · fixed in 5.15.212; From 5.16.0 · fixed in 6.1.178; From 6.2.0 · fixed in 6.6.145; From 6.7.0 · fixed in 6.12.97; From 6.13.0 · fixed in 6.18.40; From 6.19.0 · fixed in 7.1.5

References 8