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

[Hillf Danton]

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@xxxxxxxxx>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> ---

Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>