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.
