linux-kernel - Re: [PATCH 0/3] aio: ctx->dead cleanups

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:	Wed, 17 Jun 2015 03:22:45 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Jeff Moyer <jmoyer@...hat.com>, linux-aio@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] aio: ctx->dead cleanups

On 06/17, Al Viro wrote:
>
> On Wed, Jun 17, 2015 at 01:39:06AM +0100, Al Viro wrote:
>
> > Huh?  kill_ioctx() picks ctx->mmap_base and passes it to vm_munmap().
> > Which tries to grab mmap_sem, blocks for mremap() from another thread
> > and waits for it to drop mmap_sem.  By that time ctx->mmap_base has
> > nothing whatsoever to the argument we'd passed to vm_munmap().  Sure,
> > it had been recalculated by aio_ring_remap(), but it's too late for
> > us - we'd already fetched the old value.
>
> And yes, the leak you've spotted is real, but I would very much prefer
> to avoid that goto - something like this instead:
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 034e2d3..b36b530 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -291,7 +291,10 @@ static unsigned long move_vma(struct vm_area_struct *vma,
>  		if (err < 0) {
>  			move_page_tables(new_vma, new_addr, vma, old_addr,
>  					 moved_len, true);
> -			return err;
> +			vma = new_vma;
> +			old_len = new_len;
> +			old_addr = new_addr;
> +			new_addr = err;

Personally, I'd really prefer to factor out at least this
move_page_tables() with six args. Although I agree, "goto previous_if"
doesn't look nice too, this needs cleanup.

But this is minor. I am already sleeping, most probably I misread
this code. But it seems that there is another bug with VM_ACCOUNT.

I'll recheck tomorrow and write another email.

Oleg.

--
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/