[PATCH AUTOSEL 4.4 07/31] reiserfs: add check for invalid 1st journal block

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From: Pavel Skripkin <paskripkin@xxxxxxxxx>

[ Upstream commit a149127be52fa7eaf5b3681a0317a2bbb772d5a9 ]

syzbot reported divide error in reiserfs.
The problem was in incorrect journal 1st block.

Syzbot's reproducer manualy generated wrong superblock
with incorrect 1st block. In journal_init() wasn't
any checks about this particular case.

For example, if 1st journal block is before superblock
1st block, it can cause zeroing important superblock members
in do_journal_end().

Link: https://lore.kernel.org/r/20210517121545.29645-1-paskripkin@xxxxxxxxx
Reported-by: syzbot+0ba9909df31c6a36974d@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Pavel Skripkin <paskripkin@xxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
 fs/reiserfs/journal.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c
index 00985f9db9f7..6a0fa0cdc1ed 100644
--- a/fs/reiserfs/journal.c
+++ b/fs/reiserfs/journal.c
@@ -2770,6 +2770,20 @@ int journal_init(struct super_block *sb, const char *j_dev_name,
 		goto free_and_return;
+	/*
+	 * Sanity check to see if journal first block is correct.
+	 * If journal first block is invalid it can cause
+	 * zeroing important superblock members.
+	 */
+		reiserfs_warning(sb, "journal-1393",
+				 "journal 1st super block is invalid: 1st reserved block %d, but actual 1st block is %d",
+		goto free_and_return;
+	}
 	if (journal_init_dev(sb, journal, j_dev_name) != 0) {
 		reiserfs_warning(sb, "sh-462",
 				 "unable to initialize journal device");

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