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[80.251.214.228]) by smtp.gmail.com with ESMTPSA id k15-20020a170902c40f00b001869b988d93sm12154909plk.187.2022.12.21.18.02.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Dec 2022 18:02:37 -0800 (PST) From: Jun Nie To: tytso@mit.edu, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] ext4: fix underflow in group bitmap calculation Date: Thu, 22 Dec 2022 10:02:44 +0800 Message-Id: <20221222020244.1821308-1-jun.nie@linaro.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1752879178154607870?= X-GMAIL-MSGID: =?utf-8?q?1752879178154607870?= There is case that s_first_data_block is not 0 and block nr is smaller than s_first_data_block when calculating group bitmap during allocation. This underflow make index exceed es->s_groups_count in ext4_get_group_info() and trigger the BUG_ON. Fix it with protection of underflow. Fixes: 72b64b594081ef ("ext4 uninline ext4_get_group_no_and_offset()") Link: https://syzkaller.appspot.com/bug?id=79d5768e9bfe362911ac1a5057a36fc6b5c30002 Reported-by: syzbot+6be2b977c89f79b6b153@syzkaller.appspotmail.com Signed-off-by: Jun Nie --- fs/ext4/balloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c index 8ff4b9192a9f..177ef6bd635a 100644 --- a/fs/ext4/balloc.c +++ b/fs/ext4/balloc.c @@ -56,7 +56,8 @@ void ext4_get_group_no_and_offset(struct super_block *sb, ext4_fsblk_t blocknr, struct ext4_super_block *es = EXT4_SB(sb)->s_es; ext4_grpblk_t offset; - blocknr = blocknr - le32_to_cpu(es->s_first_data_block); + blocknr = blocknr > le32_to_cpu(es->s_first_data_block) ? + blocknr - le32_to_cpu(es->s_first_data_block) : 0; offset = do_div(blocknr, EXT4_BLOCKS_PER_GROUP(sb)) >> EXT4_SB(sb)->s_cluster_bits; if (offsetp)