linux-kernel - Re: KASAN: use-after-free Read in __do_page

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Date:   Tue, 31 Oct 2017 20:15:06 +0100
From:   Andrea Arcangeli <aarcange@...hat.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot 
        <bot+6a5269ce759a7bb12754ed9622076dc93f65a1f6@...kaller.appspotmail.com>,
        Jan Beulich <JBeulich@...e.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        ldufour@...ux.vnet.ibm.com, LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        syzkaller-bugs@...glegroups.com,
        Thomas Gleixner <tglx@...utronix.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Hugh Dickins <hughd@...gle.com>,
        David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thorsten Leemhuis <regressions@...mhuis.info>
Subject: Re: KASAN: use-after-free Read in __do_page_fault

On Tue, Oct 31, 2017 at 03:28:26PM +0100, Vlastimil Babka wrote:
> Hmm that could indeed work, Dmitry can you try the patch below?
> But it still seems rather fragile so I'd hope Andrea can do it more
> robust, or at least make sure that we don't reintroduce this kind of
> problem in the future (explicitly set vma to NULL with a comment?).

Reviewed-by: Andrea Arcangeli <aarcange@...hat.com>

> 
> ----8<----
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index e2baeaa053a5..9bd16fc621db 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1441,6 +1441,7 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
>  	 * the fault.  Since we never set FAULT_FLAG_RETRY_NOWAIT, if
>  	 * we get VM_FAULT_RETRY back, the mmap_sem has been unlocked.
>  	 */
> +	pkey = vma_pkey(vma);
>  	fault = handle_mm_fault(vma, address, flags);
>  	major |= fault & VM_FAULT_MAJOR;
>  
> @@ -1467,7 +1468,6 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
>  		return;
>  	}
>  
> -	pkey = vma_pkey(vma);
>  	up_read(&mm->mmap_sem);
>  	if (unlikely(fault & VM_FAULT_ERROR)) {
>  		mm_fault_error(regs, error_code, address, &pkey, fault);
>