linux-kernel - Re: [PATCH] hugetlbfs: fix offset overflow in huegtlbfs mmap

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Date:   Wed, 12 Apr 2017 11:13:20 +0800
From:   "Hillf Danton" <hillf.zj@...baba-inc.com>
To:     "'Mike Kravetz'" <mike.kravetz@...cle.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Cc:     "'Vegard Nossum'" <vegard.nossum@...il.com>,
        "'Dmitry Vyukov'" <dvyukov@...gle.com>,
        "'Michal Hocko'" <mhocko@...e.com>,
        "'Kirill A . Shutemov'" <kirill.shutemov@...ux.intel.com>,
        "'Andrey Ryabinin'" <aryabinin@...tuozzo.com>,
        "'Naoya Horiguchi'" <n-horiguchi@...jp.nec.com>,
        "'Andrew Morton'" <akpm@...ux-foundation.org>
Subject: Re: [PATCH] hugetlbfs: fix offset overflow in huegtlbfs mmap

On April 12, 2017 6:52 AM Mike Kravetz wrote: 
> 
> If mmap() maps a file, it can be passed an offset into the file at
> which the mapping is to start.  Offset could be a negative value when
> represented as a loff_t.  The offset plus length will be used to
> update the file size (i_size) which is also a loff_t.  Validate the
> value of offset and offset + length to make sure they do not overflow
> and appear as negative.
> 
> Found by syzcaller with commit ff8c0c53c475 ("mm/hugetlb.c: don't call
> region_abort if region_chg fails") applied.  Prior to this commit, the
> overflow would still occur but we would luckily return ENOMEM.
> To reproduce:
> mmap(0, 0x2000, 0, 0x40021, 0xffffffffffffffffULL, 0x8000000000000000ULL);
> 
> Resulted in,
> kernel BUG at mm/hugetlb.c:742!
> Call Trace:
>  hugetlbfs_evict_inode+0x80/0xa0
>  ? hugetlbfs_setattr+0x3c0/0x3c0
>  evict+0x24a/0x620
>  iput+0x48f/0x8c0
>  dentry_unlink_inode+0x31f/0x4d0
>  __dentry_kill+0x292/0x5e0
>  dput+0x730/0x830
>  __fput+0x438/0x720
>  ____fput+0x1a/0x20
>  task_work_run+0xfe/0x180
>  exit_to_usermode_loop+0x133/0x150
>  syscall_return_slowpath+0x184/0x1c0
>  entry_SYSCALL_64_fastpath+0xab/0xad
> 
> Reported-by: Vegard Nossum <vegard.nossum@...il.com>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> ---

Acked-by: Hillf Danton <hillf.zj@...baba-inc.com>