From: Michal Hocko <mhocko@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: miles.chen@mediatek.com,
Matthias Brugger <matthias.bgg@gmail.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
wsd_upstream@mediatek.com, linux-mediatek@lists.infradead.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] mm/page_owner: use vmalloc instead of kmalloc
Date: Fri, 26 Oct 2018 12:56:56 +0200 [thread overview]
Message-ID: <20181026085410.GA8277@dhcp22.suse.cz> (raw)
In-Reply-To: <20181025192701.GK25444@bombadil.infradead.org>
On Thu 25-10-18 12:27:01, Matthew Wilcox wrote:
> On Fri, Oct 26, 2018 at 02:34:41AM +0800, miles.chen@mediatek.com wrote:
> > The kbuf used by page owner is allocated by kmalloc(),
> > which means it can use only normal memory and there might
> > be a "out of memory" issue when we're out of normal memory.
> >
> > Use vmalloc() so we can also allocate kbuf from highmem
> > on 32bit kernel.
>
> ... hang on, there's a bigger problem here.
>
> static const struct file_operations proc_page_owner_operations = {
> .read = read_page_owner,
> };
>
> read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
> {
> ...
> return print_page_owner(buf, count, pfn, page,
> page_owner, handle);
> }
>
> static ssize_t
> print_page_owner(char __user *buf, size_t count, unsigned long pfn,
> struct page *page, struct page_owner *page_owner,
> depot_stack_handle_t handle)
> {
> ...
> kbuf = kmalloc(count, GFP_KERNEL);
>
> So I can force the kernel to make an arbitrary size allocation, triggering
> OOMs and forcing swapping if I can get a file handle to this file.
> The only saving grace is that (a) this is a debugfs file and (b) it's
> root-only (mode 0400). Nevertheless, I feel some clamping is called
> for here. Do we really need to output more than 4kB worth of text here?
Completely agreed. Let's just clamp it to a single page. Userspace can
easily loop around the syscall.
--
Michal Hocko
SUSE Labs
prev parent reply other threads:[~2018-10-26 10:57 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-25 18:34 [PATCH] mm/page_owner: use vmalloc instead of kmalloc miles.chen
2018-10-25 18:44 ` Joe Perches
2018-10-26 8:01 ` Miles Chen
2018-10-25 19:27 ` Matthew Wilcox
2018-10-26 8:50 ` Miles Chen
2018-10-26 10:56 ` Michal Hocko [this message]
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