[PATCH] bcachefs: Fix oob in bch2_dev_journal_init

[Lizhi Xu]

When journal v2 entry nr overflow, it will cause the value of ja->nr to
be incorrect, this will result in the allocated memory to ja->buckets
being too small, leading to out of bounds access.

Reported-by: syzbot+47ecc948aadfb2ab3efc@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=47ecc948aadfb2ab3efc
Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
---
 fs/bcachefs/journal.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/bcachefs/journal.c b/fs/bcachefs/journal.c
index 13669dd0e375..d4fb5a23b3f6 100644
--- a/fs/bcachefs/journal.c
+++ b/fs/bcachefs/journal.c
@@ -1307,8 +1307,18 @@ int bch2_dev_journal_init(struct bch_dev *ca, struct bch_sb *sb)
 	if (journal_buckets_v2) {
 		unsigned nr = bch2_sb_field_journal_v2_nr_entries(journal_buckets_v2);
 
-		for (unsigned i = 0; i < nr; i++)
+		for (unsigned i = 0; i < nr; i++) {
 			ja->nr += le64_to_cpu(journal_buckets_v2->d[i].nr);
+			if (le64_to_cpu(journal_buckets_v2->d[i].nr) > UINT_MAX) {
+				struct bch_fs *c = ca->fs;
+				struct printbuf buf = PRINTBUF;
+				prt_printf(&buf, "journal v2 entry d[%u].nr %lu overflow!\n", i,
+					le64_to_cpu(journal_buckets_v2->d[i].nr));
+				bch_info(c, "%s", buf.buf);
+				printbuf_exit(&buf);
+				return -BCH_ERR_ENOMEM_dev_journal_init;
+			}
+		}
 	} else if (journal_buckets) {
 		ja->nr = bch2_nr_journal_buckets(journal_buckets);
 	}
-- 
2.43.0