On Tue, Jan 12, 2021 at 11:46:55AM +0100, Jessica Yu wrote: > +++ Adam Zabrocki [12/01/21 01:15 +0100]: > > Hello, > > > > On Mon, Jan 11, 2021 at 03:20:48PM +0100, Jessica Yu wrote: > > > +++ Adam Zabrocki [10/01/21 18:54 +0100]: > > > > Hello, > > > > > > > > I believe that the following commit does introduce a gentle > > > > "functionality > > > > bug": > > > > > > > > "module: delay kobject uevent until after module init call": > > > > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/kernel/module.c?id=38dc717e97153e46375ee21797aa54777e5498f3 > > > > > > > > The official Linux Kernel API for the kernel module activities > > > > notification has > > > > been divided based on the readiness 'stage' for such module. We have the > > > > following stages: > > > > > > > > MODULE_STATE_LIVE, /* Normal state. */ > > > > MODULE_STATE_COMING, /* Full formed, running module_init. */ > > > > MODULE_STATE_GOING, /* Going away. */ > > > > MODULE_STATE_UNFORMED, /* Still setting it up. */ > > > > > > > > LIVE means that the kernel module is correctly running and all > > > > initialization > > > > work has been already done. Otherwise, we have event 'COMING' or > > > > 'UNFORMED'. > > > > > > > > In the described commit, creation of the KOBJECT has been moved after > > > > invoking > > > > a notficiation of the newly formed kernel module state (LIVE). That's > > > > somehow > > > > inconsistent from my understanding of the kernel modules notifiers > > > > logic. > > > > Creation of the new objects (like KOBJ) should be done before > > > > notification of > > > > the stage LIVE is invoked. > > > > > > I'm confused. We're not creating any kobjects here. That is all done > > > in mod_sysfs_setup(), which is called while the module is still > > > COMING. What that commit does is delay telling userspace about the > > > module (specifically, systemd/udev) until the module is basically > > > ready. Systemd was basically receiving the uevent too early, before > > > the module has initialized, hence we decided to delay the uevent [1]. > > > > > > > Sorry for the confusion on my side. I was referring to the internal state of > > the KOBJ itself which is being actively modified when uevent is sent. During > > the module creation KOBJ_ADD modifies 'kobj->state_add_uevent_sent'. Until > > recent commit, kernel didn't modify KOBJ after sending LIVE notification. > > > > > > This commit breaks some of the projects that rely on the LIVE > > > > notification to > > > > monitor when the newly loaded module is ready. > > > > > > Hm, could you please explain specifically what is the issue you're seeing? > > > What projects is it breaking? > > > > > > > I'm specifically referencing these projects which are tracking kernel > > modules > > for integrity purpose (e.g. anti-rootkit tools) like Linux Kernel Runtime > > Guard. > > It is possible to modify these tools to adopt and take into account > > modification of KOBJ after LIVE state notification. However, from my > > understanding of the kernel modules notifiers logic, KOBJ should be fully > > formed at this stage. > > Ah I see, thanks for the clarification. I was under the impression > that kobj->state_add_uevent_sent is an internal field interesting > only to lib/kobject.c, and did not know tools like you mention are > implicitly tracking that.
There is no in-kernel tools/users tracking stuff like this, so this is not an issue. The internals of kobjects can change at any time, there is no "stable api" here at all. thanks, greg k-h
