Messages in this thread | | | Date | Tue, 4 Feb 2014 15:10:25 -0500 | From | Steven Rostedt <> | Subject | Re: [RFC][PATCH] exec: Fix use after free of tracepoint trace_sched_process_exec |
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On Tue, 4 Feb 2014 20:00:07 +0100 Oleg Nesterov <oleg@redhat.com> wrote:
> On 02/04, Steven Rostedt wrote: > > > > Now to fix this we need to save the filename before calling > > search_binary_handler(). But we don't want to save it if we are not > > tracing. Why slow everyone else down? > > Yes, but it would be much simpler to dup filename unconditionally.
I was hoping not to add more work to exec, for the purpose if tracing is enabled.
> > Note also that in this case we can kill linux_binprm->tcomm[] and > simplify filename_to_taskname(). > > > This works, but is rather ugly. > > Yes ;) > > > Looking for any other suggestions here. > > Perhaps we can change flush_old_exec() to do > > if (!current->mm) { > bprm->filename = kstrdup(bprm->filename); > if (bprm->filename) > bprm->filename_was_dupped = true; // for free_bprm() > else > bprm->filename = "//enomem"; > } > > This won't penalize the normal exec, and this should fix the problem > afaics.
Don't forget to add the free. And in any case, we added a branch conditional. Yes, I'm that anal.
> > Perhaps, instead of "//enomem" flush_old_exec() should simply fail, > in this case we can kill bprm->tcomm[] too.
We could just add "//enomem" to the tracepoint too, and not use tcomm.
Also, I'm working on a patch that gets rid of all the setup of the static_key and reuses the tracepoint static key instead (suggested by Peter Zijlstra).
Thus, the change in exec.c would just look like this:
if (tracepoint_enabled(sched_process_exec)) { [...] } else ret = search_binary_handler(bprm);
That is, we can get rid of the sched_process_exec_key_reg and unreg functions, and just use this and it would become the same thing.
This will be helpful in other places too (David, I'm talking to you ;-)
-- Steve
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