reiserfs: add check for invalid 1st journal block
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().
Reported-by: syzbot+0ba9909df31c6a36974d@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Change-Id: I39f316fbc8925c8c35c95808181934645b7fdbe2
diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c
index 9edc8e2..7d5c7d3 100644
--- a/fs/reiserfs/journal.c
+++ b/fs/reiserfs/journal.c
@@ -2758,6 +2758,21 @@
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_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");
