squashfs: verify inode mode when loading from disk

squashfs: verify inode mode when loading from disk

The inode mode loaded from corrupted disk might by error contain the file
type bits.  Since the file type bits are set by squashfs_read_inode()
using bitwise OR, the file type bits must not be set by
squashfs_new_inode() from squashfs_read_inode(); otherwise, an invalid
file type bits later confuses may_open().

Link: https://lkml.kernel.org/r/f63d8d11-2254-4fc3-9292-9a43a93b374e@I-love.SAKURA.ne.jp
Reported-by: syzbot <syzbot+895c23f6917da440ed0d@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=895c23f6917da440ed0d
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Phillip Lougher <phillip@squashfs.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>