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From: William Kucharski <william.kucharski@oracle.com>
To: "Isaac J. Manjarres" <isaacm@codeaurora.org>
Cc: Kees Cook <keescook@chromium.org>,
	crecklin@redhat.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, psodagud@codeaurora.org,
	tsoni@codeaurora.org, stable@vger.kernel.org
Subject: Re: [PATCH] mm/usercopy: Use memory range to be accessed for wraparound check
Date: Wed, 14 Nov 2018 03:35:25 -0700	[thread overview]
Message-ID: <FFE931C2-DE41-4AD8-866B-FD37C1493590@oracle.com> (raw)
In-Reply-To: <1542156686-12253-1-git-send-email-isaacm@codeaurora.org>



> On Nov 13, 2018, at 5:51 PM, Isaac J. Manjarres <isaacm@codeaurora.org> wrote:
> 
> diff --git a/mm/usercopy.c b/mm/usercopy.c
> index 852eb4e..0293645 100644
> --- a/mm/usercopy.c
> +++ b/mm/usercopy.c
> @@ -151,7 +151,7 @@ static inline void check_bogus_address(const unsigned long ptr, unsigned long n,
> 				       bool to_user)
> {
> 	/* Reject if object wraps past end of memory. */
> -	if (ptr + n < ptr)
> +	if (ptr + (n - 1) < ptr)
> 		usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n);

I'm being paranoid, but is it possible this routine could ever be passed "n" set to zero?

If so, it will erroneously abort indicating a wrapped address as (n - 1) wraps to ULONG_MAX.

Easily fixed via:

	if ((n != 0) && (ptr + (n - 1) < ptr))

William Kucharski

  reply	other threads:[~2018-11-14 10:35 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-14  0:51 [PATCH] mm/usercopy: Use memory range to be accessed for wraparound check Isaac J. Manjarres
2018-11-14 10:35 ` William Kucharski [this message]
2018-11-14 11:09   ` David Laight
2018-11-14 11:46     ` William Kucharski
2018-11-14 17:32       ` isaacm
2018-11-14 22:50         ` William Kucharski
2018-11-14 23:27   ` Kees Cook
2018-11-14 23:32 ` Kees Cook
2018-11-15  7:05 ` Sasha Levin
2019-07-30 17:54 Isaac J. Manjarres
2019-07-31 20:25 ` Kees Cook

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