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Date: Sat, 23 Jul 2022 16:43:11 +0200 From: Greg KH <gregkh@...uxfoundation.org> To: Siddh Raman Pant <code@...dh.me> Cc: David Howells <dhowells@...hat.com>, Jarkko Sakkinen <jarkko@...nel.org>, James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, linux-security-modules <linux-security-module@...r.kernel.org>, keyrings <keyrings@...r.kernel.org>, linux-kernel-mentees <linux-kernel-mentees@...ts.linuxfoundation.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] keys/keyctl: Use kfree_rcu instead of kfree On Sat, Jul 23, 2022 at 08:05:27PM +0530, Siddh Raman Pant wrote: > On Sat, 23 Jul 2022 19:35:16 +0530 Greg KH <gregkh@...uxfoundation.org> wrote: > > That does not explain why this change is needed. What problem does this > > solve? Why use RCU if you don't have to? What functionality did you > > just change in this commit and why? > > We can avoid a race condition wherein some process tries to access them while > they are being freed. For instance, the comment on `watch_queue_clear()` also > states that: > /* > * Remove all the watches that are contributory to a queue. This has the > * potential to race with removal of the watches by the destruction of the > * objects being watched or with the distribution of notifications. > */ > And an RCU read critical section is initiated in that function, so we should > use kfree_rcu() to not unintentionally free it while it is in the critical > section. You need to explain all of this in a changelog text. Don't say what you do, but say why you are doing it. > > And how was this tested? > > It compiles locally for me, and I used syzbot on this along with testing the > other `watch_queue_clear` patch, which generated no errors. How does the watch queue stuff relate to this keyctl logic? Again, be specific as to why you are doing things. thanks, greg k-h
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