Messages in this thread | | | Date | Thu, 25 Oct 2018 12:27:01 -0700 | From | Matthew Wilcox <> | Subject | Re: [PATCH] mm/page_owner: use vmalloc instead of kmalloc |
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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?
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