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Re: /tmp usage and security

On Thu, 9 Oct 1997, Andrea Mennucci wrote:

> I think that there is no easy patch to these situations;
> here are a few proposals for developers
> 
> 1) Before a program creates a files in /tmp, 
>    it checks if there is already one with the same name, and unlinks it
>    or it change the chosen name for the file
> 2) All temporary files that are created should be of the form
>    name.$$.$rand
>    where $$ is the pid number and $rand is a random string of 8 characters;
I think that the correct solution is prohibit scripts using the tmp. They
should have their own dir under /var/* , and have that owned the runner of the
script. It is sometimes not a good solution, I know. Another solution is
create a directory under tmp and use temporary scripts there. i recall that
it had been talked about on bugtraq, and there should be done other
precautions I forgot.
> 
> BTW
> a function in libc6 may be added, like this:
>  char *good_temp_filename(char *name)
> this function, given a name, builds a good filename for a file in /tmp/
>  using name as a prefix
> A command in /usr/bin may be created to perform the same trick for shell
> scripts.
It is not a solution either. There is a race condition involved either.
For C programs there is the mkstemp(3) call which gives a _file_descriptor_.
Providing a program which makes something like that you have proposed but
in a really safe way (creating a directory, checking it, and establishing a
file in it) seems to be a good solution.
> 
> 3) at boot time, right after the
>  rm -rf /tmp/
> a scripts creates all directories like 
>  /tmp/.users/USER 
> where  USER are all the usernames in /etc/passwd,
> with ownership to USER and mode 
>  chmod og-rwx
It is equivalent to have temp dirs for every user in their home.
> 
> good_temp_filename() check if /tmp/.users/USER exist;
> otherwise it tries to give a name that is not used.
> Programs that use this function would be safer.
> 
> I understand that doing this may be problematic; it involves 
> asking all developers/mantainers to review their code;
> but I see no easy solution to this problem.
Neither me.

---
GNU GPL: csak tiszta forrásból


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