Re: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts

[Miklos Szeredi]

> > @@ -510,10 +533,16 @@ static struct vfsmount *clone_mnt(struct
> >                                         int flag)
> >  {
> >         struct super_block *sb = old->mnt_sb;
> > -       struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
> > +       struct vfsmount *mnt;
> > 
> > +       if (flag & CL_SETUSER) {
> > +               int err = reserve_user_mount();
> > +               if (err)
> > +                       return ERR_PTR(err);
> > +       }
> > +       mnt = alloc_vfsmnt(old->mnt_devname);
> >         if (!mnt)
> > -               return ERR_PTR(-ENOMEM);
> > +               goto alloc_failed;
> > 
> >         mnt->mnt_flags = old->mnt_flags;
> >         atomic_inc(&sb->s_active); 
> 
> I think there's a little race here.  We could have several users racing
> to get to this point when nr_user_mounts==max_user_mounts-1.  One user
> wins the race and gets their mount reserved.  The others get the error
> out of reserve_user_mount(), and return.
> 
> But, the winner goes on to error out on some condition further down in
> clone_mnt() and never actually instantiates the mount.
> 
> Do you think this is a problem?

For similar reasons as stated in the previous mail, I don't think this
matters.  If nr_user_mounts is getting remotely close to
max_user_mounts, then something is wrong (or the max needs to be
raised anyway).

Thanks for the review, Dave!

Miklos
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/