Re: [PATCH 0/9] proc: protect /proc/<pid>/* files across execve

[Linus Torvalds <torvalds@linux-foundation.org>]

On Sat, Mar 10, 2012 at 3:25 PM, Djalal Harouni <tixxdz@opendz.org> wrote:
>
> 1) Use the target exec_id to bind files to their exec_id task:
>
> For the REG files /proc/<pid>/{environ,pagemap,mem} we set the exec_id
> of the proc_file_private to the target task, and we continue with
> permission checks at open time, later on each read/write call the
> permission checks are done + check the target exec_id if it equals the
> exec_id of the proc_file_private that was set at open time, in other words
> we bind the file to its task's exec_id, this way new exec programs can not
> operate on the passed fd.

So the exec_id approach was totally broken when it was used for
/proc/<pid>/mem, is there any reason to believe it's a good idea now?

It's entirely predictable, and you can make the exec_id match by
simply forking elsewhere and then passing the fd around using unix
domain sockets, since the exec_id is just updated by incrementing a
counter.

I would in general suggest strongly against using exec_id for anything
that involves files. It isn't designed for that, it's designed for the
whole "check the parent exec_id" thing for ptrace, where that whole
"pass things around to another process" approach doesn't work.

                Linus