linux-kernel - Re: [PATCH] arch/x86: fix out-of-bounds in get

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Message-ID: <CAPAsAGwyUQc6UffyQ=vJSNwOYQWE9XMzK5dT__C4r5_+qEYfHA@mail.gmail.com>
Date:	Mon, 28 Sep 2015 18:40:30 +0300
From:	Andrey Ryabinin <ryabinin.a.a@...il.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>, ak@...ux.intel.com,
	kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH] arch/x86: fix out-of-bounds in get_wchan()

2015-09-28 12:00 GMT+03:00 Dmitry Vyukov <dvyukov@...gle.com>:
>         stack = (unsigned long)task_stack_page(p);
> -       if (p->thread.sp < stack || p->thread.sp >= stack+THREAD_SIZE)
> +       /* The task can be already running at this point, so tread carefully. */
> +       fp = READ_ONCE(p->thread.sp);
> +       if (fp < stack || fp >= stack+THREAD_SIZE)

Since we deference fp, it should be "|| fp + sizeof(u64) >= stack + THREAD_SIZE"

>                 return 0;
> -       fp = *(u64 *)(p->thread.sp);
> +       fp = READ_ONCE(*(u64 *)fp);
>         do {
>                 if (fp < (unsigned long)stack ||
> -                   fp >= (unsigned long)stack+THREAD_SIZE)
> +                   fp+8 >= (unsigned long)stack+THREAD_SIZE)

The same as above;
        'fp+8 +sizeof(u64) >= ...'

>                         return 0;
> -               ip = *(u64 *)(fp+8);
> +               ip = READ_ONCE(*(u64 *)(fp+8));
>
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