linux-kernel - Re: *sigh* /proc/*/pagemap

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Date:	Sat, 5 Jul 2008 11:44:54 +0400
From:	"Alexey Dobriyan" <adobriyan@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	torvalds@...uxfoundation.org, akpm@...uxfoundation.org,
	mpm@...enic.com, linux-kernel@...r.kernel.org
Subject: Re: *sigh* /proc/*/pagemap

On 7/5/08, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Sat, 5 Jul 2008 05:07:02 +0400 "Alexey Dobriyan" <adobriyan@...il.com>
> wrote:

>> 3) unstatic struct pagemap_walk, so two threads won't fsckup each other
>>    (including those started by root, including flipping ->mm when you
>> don't have permissions),
>
> Below

Below.

>> 4) remove second ptrace_may_attach(), and
>
> Can't find what you're referring to here.

pagemap_read() contains two calls to ptrace_may_attach(),
second one looks unneeded.

>> 5) check with microscope allocation there -- page-aligned address and size
>> == 0
>>     should allocate 0 bytes, and
>
> Where?

kmalloc() in pagemap_read(). kmalloc(0)  and integer wraparound look possible.

>> 6) actually check that it works.
>
> Will have a shot.

Ha-ha!

> - unstatic struct pagemap_walk, so two threads won't fsckup each other
>   (including those started by root, including flipping ->mm when you don't
>   have permissions)

> --- a/fs/proc/task_mmu.c~pagemap-fixes-to-pagemap_read
> +++ a/fs/proc/task_mmu.c
> @@ -641,6 +636,7 @@ static ssize_t pagemap_read(struct file
>  	struct pagemapread pm;
>  	int pagecount;
>  	int ret = -ESRCH;
> +	static struct mm_walk pagemap_walk;

No, can't have static here, two threads doing pagemap_read() will overwrite
each other's .mm and "out" at least. Like "pm" it shouldn't be global.

It doesn't oops here for unknown reasons, though.

> @@ -684,6 +681,11 @@ static ssize_t pagemap_read(struct file
>  	pm.out = (u64 *)buf;
>  	pm.end = (u64 *)(buf + count);
>
> +	pagemap_walk.pmd_entry = pagemap_pte_range;
> +	pagemap_walk.pte_hole = pagemap_pte_hole;
> +	pagemap_walk.mm = mm;
> +	pagemap_walk.private = &pm;
--
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