[PATCH 4.19 237/421] reiserfs: add check for invalid 1st journal block

Greg Kroah-Hartman
2021-07-19T16:18:37Z

From: Pavel Skripkin <paskripkin@gmail.com>

[ 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@gmail.com
Reported-by: syzbot+0ba9909df31c6a36974d@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/reiserfs/journal.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c
index 8a76f9d14bc6..78be6dbcd762 100644
--- a/fs/reiserfs/journal.c
+++ b/fs/reiserfs/journal.c
@@ -2772,6 +2772,20 @@ 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.
+ */
+ if (!SB_ONDISK_JOURNAL_DEVICE(sb) &&
+ SB_ONDISK_JOURNAL_1st_BLOCK(sb) < SB_JOURNAL_1st_RESERVED_BLOCK(sb)) {
+ reiserfs_warning(sb, "journal-1393",
+ "journal 1st super block is invalid: 1st reserved block %d, but actual 1st block is %d",
+ SB_JOURNAL_1st_RESERVED_BLOCK(sb),
+ SB_ONDISK_JOURNAL_1st_BLOCK(sb));
+ goto free_and_return;
+ }
+
if (journal_init_dev(sb, journal, j_dev_name) != 0) {
reiserfs_warning(sb, "sh-462",
"unable to initialize journal device");
--
2.30.2