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SubjectRe: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts
From
Date
> > @@ -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


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