[icedtea-web] RFC: reduce permissions on created files

Omair Majid omajid at redhat.com
Tue Nov 23 11:54:41 PST 2010

On 11/22/2010 03:31 PM, Deepak Bhole wrote:
> * Omair Majid<omajid at redhat.com>  [2010-11-12 09:46]:
>> On 11/12/2010 06:54 AM, Dr Andrew John Hughes wrote:
>>> On 20:14 Thu 11 Nov     , Omair Majid wrote:
>>>> Hi,
>>>> The attached patch tries to make files created by netx/plugin more
>>>> secure by removing unnecessary permissions. IcedTea6 used to carry a
>>>> patch to change the umask used by the javaws process which IcedTea-Web
>>>> does not. This patch tries to make netx/plugin behave like they would in
>>>> the presence of such a patch.
>>>> This patch does not change the file permissions on files that are cached
>>>> (mostly because I dont see why they should be protected), but does
>>>> change permissions on KeyStores, native directories created under /tmp/,
>>>> lock files, files created through the JNLP api and log files.
>>> I think this is a better approach, though we should be aware that the permissions
>>> are now changed after the file has been created, whereas before (I presume) they
>>> were created with the correct permissions to begin with.
>> Hm... Does creating a new (blank) file, setting appropriate
>> permissions on it and then writing content to it ensure that the
>> content can not be seen by others? This was the original intent with
>> this patch (I have since noticed one mistake in the patch). If
>> creating a blank file, setting permissions on it and then writing
>> actual content does not ensure the confidentiality of the data, then
>> I would like to find another way to accomplish this.
>> Thanks for looking over the patch.
> Good point Andrew! This patch needs to be modified. If a file is created
> with og+[r|w|x] and then restricted, anything that opened the handle
> before the change will have the permissions it did when the handle was
> opened. We need to create the file under a different (temp) name, change
> permissions, and then move it. AFAIK that shouldn't allow access.
> Access bypass can be verified as follows:
> 1. Create a file as one user (A), allow a+r
> 2. tail -f that file as another user (B)
> 3. As A, og-rwx the file
> 4. As A, write to the file
> The tail -f command from #2 will show the output, thus confirming that
> user B has access when they shouldn't.
> tail -f no longer gets the info if the file is renamed to something else
> between step 3 and 4.

Thanks for the name change idea. The attached patch implements it. Thoughts?

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