Re: [RCF] [PATCH] unprivileged mount/umount

[Miklos Szeredi <miklos@szeredi.hu>]

> > >  	dentry = file->f_dentry;
> > >  	mnt = file->f_vfsmnt;
> > >  	inode = dentry->d_inode;
> > > +	if(mnt->mnt_namespace != current->namespace)
> > > +		goto out_putf;
> > >  
> > >  	error = -ENOTDIR;
> > >  	if (!S_ISDIR(inode->i_mode))
> > > 
> > 
> > Does this actually fix the problem?  The open is done in the right
> > namespace, and mount() doesn't call open().
> 
> Right but this fix disallows fchdir into a directory belonging to
> a different namespace.  And hence would disallow the ability to
> cross mount across namespaces.

Ahh, sorry.  I thought that check was in open(), but I see now it's in
fchdir().  Next time please use '-p' option of diff, to avoid
confusing thoughtless readers like me :)

Though your patch does fix the bug, I still think it's wrong, since
mounting from a different namespace has legitimate uses, and is not a
security problem.

Miklos
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