Re: [syzbot] [bcachefs?] KASAN: slab-out-of-bounds Read in journal_entry_dev_usage_to_text

[Edward Adam Davis]

entry data bytes too small 

#syz test: upstream 1722389b0d86

diff --git a/fs/bcachefs/bcachefs_format.h b/fs/bcachefs/bcachefs_format.h
index e3b1bde489c3..d536da101e89 100644
--- a/fs/bcachefs/bcachefs_format.h
+++ b/fs/bcachefs/bcachefs_format.h
@@ -1252,6 +1252,11 @@ struct jset_entry_dev_usage {
 
 static inline unsigned jset_entry_dev_usage_nr_types(struct jset_entry_dev_usage *u)
 {
+	if (vstruct_bytes(&u->entry) < sizeof(struct jset_entry_dev_usage)) {
+		pr_info("entry data bytes %u is too small", vstruct_bytes(&u->entry));
+		return 0;
+	}
+
 	return (vstruct_bytes(&u->entry) - sizeof(struct jset_entry_dev_usage)) /
 		sizeof(struct jset_entry_dev_usage_type);
 }
-- 
2.43.0