On Thu, Apr 28, 2022 at 04:45:05AM +0000, Al Viro wrote:
> On Wed, Apr 27, 2022 at 11:22:01AM +0200, Christian Brauner wrote:
>
> > +static inline umode_t vfs_prepare_mode(struct user_namespace *mnt_userns,
> > + const struct inode *dir, umode_t mode,
> > + umode_t mask_perms, umode_t type)
> > +{
> > + /*
> > + * S_ISGID stripping depends on the mode of the new file so make sure
> > + * that the caller gives us this information and splat if we miss it.
> > + */
> > + WARN_ON_ONCE((mode & S_IFMT) == 0);
>
> <blink>
>
> First of all, what happens if you call mknod("/tmp/blah", 0, 0)? And the only
> thing about type bits we care about is "is it a directory" - the sensitive
> stuff is in the low 12 bits... What is that check about?
Do note that this is just an untested rough sketch to illustrate how to
move it into vfs_*() helpers.
