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Re: [PATCH v2] clear file privilege bits when mmap writing

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On Thu, Dec 3, 2015 at 5:45 PM, yalin wang <yalin.wang2010@gmail.com> wrote:
>
>> On Dec 2, 2015, at 16:03, Kees Cook <keescook@chromium.org> wrote:
>>
>> Normally, when a user can modify a file that has setuid or setgid bits,
>> those bits are cleared when they are not the file owner or a member
>> of the group. This is enforced when using write and truncate but not
>> when writing to a shared mmap on the file. This could allow the file
>> writer to gain privileges by changing a binary without losing the
>> setuid/setgid/caps bits.
>>
>> Changing the bits requires holding inode->i_mutex, so it cannot be done
>> during the page fault (due to mmap_sem being held during the fault).
>> Instead, clear the bits if PROT_WRITE is being used at mmap time.
>>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>> Cc: stable@vger.kernel.org
>> —
>
> is this means mprotect() sys call also need add this check?
> mprotect() can change to PROT_WRITE, then it can write to a
> read only map again , also a secure hole here .

Yes, good point. This needs to be added. I will send a new patch. Thanks!

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security
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[PATCH v2] fs: clear file privilege bits when mmap writing Kees Cook <keescook@chromium.org> - 2015-12-03 01:10 +0100
  Re: [PATCH v2] fs: clear file privilege bits when mmap writing Andrew Morton <akpm@linux-foundation.org> - 2015-12-03 01:20 +0100
    Re: [PATCH v2] fs: clear file privilege bits when mmap writing Kees Cook <keescook@chromium.org> - 2015-12-03 17:10 +0100
    Re: [PATCH v2] fs: clear file privilege bits when mmap writing Kees Cook <keescook@chromium.org> - 2015-12-03 19:20 +0100
  Re: [PATCH v2] clear file privilege bits when mmap writing yalin wang <yalin.wang2010@gmail.com> - 2015-12-04 02:50 +0100
    Re: [PATCH v2] clear file privilege bits when mmap writing Kees Cook <keescook@chromium.org> - 2015-12-07 23:50 +0100
      Re: [PATCH v2] clear file privilege bits when mmap writing Kees Cook <keescook@chromium.org> - 2015-12-08 01:50 +0100
        Re: [PATCH v2] clear file privilege bits when mmap writing Jan Kara <jack@suse.cz> - 2015-12-09 09:30 +0100
          Re: [PATCH v2] clear file privilege bits when mmap writing Kees Cook <keescook@chromium.org> - 2015-12-10 00:00 +0100

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