linux-kernel - Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 2 Feb 2009 11:23:33 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Hugh Dickins <hugh@...itas.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Greg KH <gregkh@...e.de>,
	Maksim Yevmenkin <maksim.yevmenkin@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	will@...wder-design.com, Rik van Riel <riel@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mikos Szeredi <miklos@...redi.hu>,
	Andy Whitcroft <apw@...onical.com>
Subject: Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED
 file segments



On Mon, 2 Feb 2009, Mel Gorman wrote:
>
> Do not account for address space usage when making hugetlbfs mappings RW
> 
> hugetlbfs accounts for its address space usage separate from the VM
> core. VM_ACCOUNT should not be set for its mappings but it is possible it gets
> set if a user creates a RO hugetlbfs mapping MAP_NORESERVE and then calls
> mprotect(). This patch stops VM_ACCOUNT being set for hugetlbfs mappings
> during mprotect().
> 
> Credit goes to Kosaki Motohiro for spotting this.
> 
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> 
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index abe2694..31ddc6a 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -153,7 +153,7 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
>  	 * but (without finer accounting) cannot reduce our commit if we
>  	 * make it unwritable again.
>  	 */
> -	if (newflags & VM_WRITE) {
> +	if (newflags & VM_WRITE && !(vma->vm_flags & VM_HUGETLB)) {

Wouldn't it be _much_ nicer to just depend on that whole VM_NORESERVE 
thing?

Those hugetlb mappings _should_ have VM_NORESERVE on them, so the 
following test:

>  		if (!(oldflags & (VM_ACCOUNT|VM_WRITE|
>  						VM_SHARED|VM_NORESERVE))) {
>  			charged = nrpages;

should do it all correctly.

Why make up some ad-hoc testing, when we already have a flag for _exactly_ 
this issue. That's what VM_NORESERVE means: don't apply VM_ACCOUNT.

IOW, I don't see the point of this patch at all.

And if there is some hugetlb path that doesn't set VM_NORESERVE, then fix 
_that_ instead.

			Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/