Date: Thu, 17 Aug 2017 07:39:26 -0700 From: Kees Cook <keescook@...gle.com> To: Thomas Gleixner <tglx@...utronix.de> Cc: LKML <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com> Subject: Re: refactoring timers to avoid init_timer*() On Thu, Aug 17, 2017 at 7:30 AM, Thomas Gleixner <tglx@...utronix.de> wrote: > On Wed, 16 Aug 2017, Kees Cook wrote: >> In the process I noticed that we already have >> scripts/coccinelle/api/setup_timer.cocci to detect existing cases of: >> >> init_timer(t); >> t->function = func; >> t->data = data; >> >> And replace it with: setup_timer(t, func, data); >> >> Another pattern was: >> >> t->expires = when; >> add_timer(t); >> >> Which can be replaced with mod_timer(t, when); >> >> So, I've created scripts/coccinelle/api/mod_timer.cocci for the >> latter, and done a few passes with manual review. The current result >> doesn't fully eliminate init_timer() yet, but it gets much closer. I >> just wanted to be sure that this whole clean-up would actually be >> welcome before I try to nail down the last many cases. > > I think it's worth the trouble, but rather than having a gazillion of > commits with the same changelog, we should do that based on a cocci script > right before the next rc1 in one go and be done with it. > > That will cover most of the init_timer() cases and we can fixup the > remaining few oddballs manually after that. Okay, that sounds good. I'll work on improving the cocci scripts. For example, I noticed that it doesn't notice having assignments _before_ the init_timer() call: timer->function = func; timer->data = data; init_timer(timer); Whee. :) BTW, I may back off on doing ->expires = when; add_timer(timer) --> mod_timer(timer, when) changes since that actually removes a sanity check in add_timer(). My plans currently are collapsing all the open-coded init_timer*()s into setup_*timer() and then adding something like aim_timer(timer, func, data) for post-setup function/data changes. -Kees > > I just noticed that we have the same pattern with hrtimer_init(). I had a > stab on adding hrtimer_setup() and friends which takes a function argument > and converted the bulk with coccinelle. > > 82 files changed, 186 insertions(+), 210 deletions(-) > > We can do that in the same sweep as the init_timer() one and then you can > do the canary magic on hrtimers as well. > > Thanks, > > tglx > > -- Kees Cook Pixel Security
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