linux-kernel - Re: [PATCH 12/13] tracing/uprobes: Add more fetch functions

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Message-ID: <20131104164431.GA10053@redhat.com>
Date:	Mon, 4 Nov 2013 17:44:31 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH 12/13] tracing/uprobes: Add more fetch functions

On 11/04, Namhyung Kim wrote:
>
> On Thu, 31 Oct 2013 19:22:18 +0100, Oleg Nesterov wrote:
> > On 10/29, Namhyung Kim wrote:
> >>
> >> +static void __user *get_user_vaddr(unsigned long addr, struct trace_uprobe *tu)
> >> +{
> >> +	unsigned long pgoff = addr >> PAGE_SHIFT;
> >> +	struct vm_area_struct *vma;
> >> +	struct address_space *mapping;
> >> +	unsigned long vaddr = 0;
> >> +
> >> +	if (tu == NULL) {
> >> +		/* A NULL tu means that we already got the vaddr */
> >> +		return (void __force __user *) addr;
> >> +	}
> >> +
> >> +	mapping = tu->inode->i_mapping;
> >> +
> >> +	mutex_lock(&mapping->i_mmap_mutex);
> >> +	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
> >> +		if (vma->vm_mm != current->mm)
> >> +			continue;
> >> +		if (!(vma->vm_flags & VM_READ))
> >> +			continue;
> >> +
> >> +		vaddr = offset_to_vaddr(vma, addr);
> >> +		break;
> >> +	}
> >> +	mutex_unlock(&mapping->i_mmap_mutex);
> >> +
> >> +	WARN_ON_ONCE(vaddr == 0);
> >
> > Hmm. But unless I missed something this "addr" passed as an argument can
> > be wrong? And if nothing else this or another thread can unmap the vma?
>
> You mean WARN_ON_ONCE here is superfluous?  I admit that it should
> protect concurrent vma [un]mappings.  Please see my reply in other
> thread for a new approach.

Whatever we do this address can be unmapped. For example, just because of
@invalid_address passed to trace_uprobe.c.

We do not really care, copy_from_user() should fail. But we should not
WARN() in this case.

Oleg.

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