Re: Directory/File Access Permissions for COPY and Generic File Access Functions

On Wed, Oct 29, 2014 at 10:52 AM, Andres Freund  wrote:
>> The larger point though is that this is just one of innumerable attack
>> routes for anyone with the ability to make the server do filesystem reads
>> or writes of his choosing.  If you think that's something you can safely
>> give to people you don't trust enough to make them superusers, you are
>> wrong, and I don't particularly want to spend the next ten years trying
>> to wrap band-aids around your misjudgment.
>
> ... but that doesn't necessarily address this point.

I think the question is "just how innumerable are those attack
routes"?  So, we can prevent a symlink from being used via O_NOFOLLOW.
But what about hard links?

In general, the hazard is that an untrusted user can induce the user
to read or write a file that the user in question could not have read
or written himself.  It's not clear to me whether it's reasonably
possible to build a system that is robust against such attacks, or
not.

-- 
Robert Haas
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