linux-kernel - Re: [PATCH v3] hugetlbfs: check for pgoff value overflow

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:   Fri, 16 Mar 2018 09:19:07 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        bugzilla-daemon@...zilla.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Nic Losby <blurbdust@...il.com>,
        Yisheng Xie <xieyisheng1@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH v3] hugetlbfs: check for pgoff value overflow

On 03/16/2018 03:17 AM, Michal Hocko wrote:
> On Thu 08-03-18 16:27:26, Mike Kravetz wrote:
> 
> OK, looks good to me. Hairy but seems to be the easiest way around this.
> Acked-by: Michal Hocko <mhocko@...e.com>
> 
<snip>
>> +/*
>> + * Mask used when checking the page offset value passed in via system
>> + * calls.  This value will be converted to a loff_t which is signed.
>> + * Therefore, we want to check the upper PAGE_SHIFT + 1 bits of the
>> + * value.  The extra bit (- 1 in the shift value) is to take the sign
>> + * bit into account.
>> + */
>> +#define PGOFF_LOFFT_MAX (PAGE_MASK << (BITS_PER_LONG - (2 * PAGE_SHIFT) - 1))

Thanks Michal,

However, kbuild found a problem with this definition on certain configs.
Consider a config where,
BITS_PER_LONG = 32 (32bit config)
PAGE_SHIFT = 16 (64K pages)
This results in the negative shift value.
Not something I would not immediately think of, but a valid config.

The definition has been changed to,
#define PGOFF_LOFFT_MAX \
	(((1UL << (PAGE_SHIFT + 1)) - 1) <<  (BITS_PER_LONG - (PAGE_SHIFT + 1)))

as discussed here,
http://lkml.kernel.org/r/432fb2a3-b729-9c3a-7d60-890b8f9b10dd@oracle.com
-- 
Mike Kravetz