Affected: Linux

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.