From: David Laight <David.Laight@ACULAB.COM>
To: 'William Kucharski' <william.kucharski@oracle.com>,
"Isaac J. Manjarres" <isaacm@codeaurora.org>
Cc: Kees Cook <keescook@chromium.org>,
"crecklin@redhat.com" <crecklin@redhat.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"psodagud@codeaurora.org" <psodagud@codeaurora.org>,
"tsoni@codeaurora.org" <tsoni@codeaurora.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH] mm/usercopy: Use memory range to be accessed for wraparound check
Date: Wed, 14 Nov 2018 11:09:25 +0000 [thread overview]
Message-ID: <5dcd06a0f84a4824bb9bab2b437e190d@AcuMS.aculab.com> (raw)
In-Reply-To: <FFE931C2-DE41-4AD8-866B-FD37C1493590@oracle.com>
From: William Kucharski
> Sent: 14 November 2018 10:35
>
> > 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))
Ugg... you don't want a double test.
I'd guess that a length of zero is likely, but a usercopy that includes
the highest address is going to be invalid because it is a kernel address
(on most archs, and probably illegal on others).
What you really want to do is add 'ptr + len' and check the carry flag.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2018-11-14 11:09 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
2018-11-14 11:09 ` David Laight [this message]
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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