In the Linux kernel, the following vulnerability has been resolved:
hfsplus: Verify inode mode when loading from disk
syzbot is reporting that S_IFMT bits of inode->i_mode can become bogus when the S_IFMT bits of the 16bits "mode" field loaded from disk are corrupted.
According to [1], the permissions field was treated as reserved in Mac OS 8 and 9. According to [2], the reserved field was explicitly initialized with 0, and that field must remain 0 as long as reserved. Therefore, when the "mode" field is not 0 (i.e. no longer reserved), the file must be S_IFDIR if dir == 1, and the file must be one of S_IFREG/S_IFLNK/S_IFCHR/ S_IFBLK/S_IFIFO/S_IFSOCK if dir == 0.