From: Junrui Luo Date: Wed, 13 May 2026 09:28:40 +0000 (+0800) Subject: jbd2: fix integer underflow in jbd2_journal_initialize_fast_commit() X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=289a2ca0c9b7eae74f93fc213b0b971669b8683d;p=thirdparty%2Flinux.git 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. Fixes: 6866d7b3f2bb ("ext4 / jbd2: add fast commit initialization") Reported-by: Yuhao Jiang Cc: stable@vger.kernel.org Signed-off-by: Junrui Luo Fixes: e029c5f27987 ("ext4: make num of fast commit blocks configurable") Reviewed-by: Baokun Li Fixes: e029c5f279872 ("ext4: make num of fast commit blocks configurable") Reviewed-by: Zhang Yi Reviewed-by: Jan Kara Link: https://patch.msgid.link/SYBPR01MB7881663C927DE9D7BBF4D1DFAF062@SYBPR01MB7881.ausprd01.prod.outlook.com Signed-off-by: Theodore Ts'o --- diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c index 4f397fcdb13c5..e3b2e38e1a1b7 100644 --- a/fs/jbd2/journal.c +++ b/fs/jbd2/journal.c @@ -2263,6 +2263,8 @@ jbd2_journal_initialize_fast_commit(journal_t *journal) unsigned long long num_fc_blks; num_fc_blks = jbd2_journal_get_num_fc_blks(sb); + if (num_fc_blks > journal->j_last) + return -EFSCORRUPTED; if (journal->j_last - num_fc_blks < JBD2_MIN_JOURNAL_BLOCKS) return -ENOSPC;