From: Jessica Yu <jeyu@redhat.com>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: shuah@kernel.org, rusty@rustcorp.com.au, ebiederm@xmission.com,
dmitry.torokhov@gmail.com, acme@redhat.com, corbet@lwn.net,
martin.wilck@suse.com, mmarek@suse.com, pmladek@suse.com,
hare@suse.com, rwright@hpe.com, jeffm@suse.com, DSterba@suse.com,
fdmanana@suse.com, neilb@suse.com, linux@roeck-us.net,
rgoldwyn@suse.com, subashab@codeaurora.org, xypron.glpk@gmx.de,
keescook@chromium.org, atomlin@redhat.com, mbenes@suse.cz,
paulmck@linux.vnet.ibm.com, dan.j.williams@intel.com,
jpoimboe@redhat.com, davem@davemloft.net, mingo@redhat.com,
akpm@linux-foundation.org, torvalds@linux-foundation.org,
linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: kmod: add a sanity check on module loading
Date: Tue, 3 Jan 2017 18:47:45 -0800 [thread overview]
Message-ID: <20170104024745.t3selvpcqcbtfxfs@jeyu> (raw)
In-Reply-To: <20161208194930.2816-1-mcgrof@kernel.org>
+++ Luis R. Rodriguez [08/12/16 11:49 -0800]:
>kmod has an optimization in place whereby if a some kernel code
>uses request_module() on a module already loaded we never bother
>userspace as the module already is loaded. This is not true for
>get_fs_type() though as it uses aliases.
>
>Additionally kmod <= v19 was broken -- it returns 0 to modprobe calls,
>assuming the kernel module is built-in, where really we have a race as
>the module starts forming. kmod <= v19 has incorrect userspace heuristics,
>a userspace kmod fix is available for it:
>
>http://git.kernel.org/cgit/utils/kernel/kmod/kmod.git/commit/libkmod/libkmod-module.c?id=fd44a98ae2eb5eb32161088954ab21e58e19dfc4
>
>This changes kmod to address both:
>
> o Provides the alias optimization for get_fs_type() so modules already
> loaded do not get re-requested.
>
> o Provides a sanity test to verify modprobe's work
>
>This is important given how any get_fs_type() users assert success
>means we're ready to go, and tests with the new test_kmod stress driver
>reveal that request_module() and get_fs_type() might fail for a few
>other reasons. You don't need old kmod to fail on request_module() or
>get_fs_type(), with the right system setup, these calls *can* fail
>today.
>
>Although this does get us in the business of keeping alias maps in
>kernel, the the work to support and maintain this is trivial.
>Aditionally, since it may be important get_fs_type() should not fail on
>certain systems, this tightens things up a bit more.
>
>The TL;DR:
>
>kmod <= v19 will return 0 on modprobe calls if you are built-in,
>however its heuristics for checking if you are built-in were broken.
>
>It assumed that having the directory /sys/module/module-name
>but not having the file /sys/module/module-name/initstate
>is sufficient to assume a module is built-in.
>
>The kernel loads the inittstate attribute *after* it creates the
>directory. This is an issue when modprobe returns 0 for kernel calls
>which assumes a return of 0 on request_module() can give you the
>right to assert the module is loaded and live.
>
>We cannot trust returns of modprobe as 0 in the kernel, we need to
>verify that modules are live if modprobe return 0 but only if modules
>*are* modules. The kernel heuristic we use to determine if a module is
>built-in is that if modprobe returns 0 we know we must be built-in or
>a module, but if we are a module clearly we must have a lingering kmod
>dangling on our linked list. If there is no modules there we are *somewhat*
>certain the module must be built in.
>
>This is not enough though... we cannot easily work around this since the
>kernel can use aliases to userspace for modules calls. For instance
>fs/namespace.c uses fs-modulename for filesystesms on get_fs_type(), so
>these need to be taken into consideration as well.
>
>Using kmod <= 19 will give you a NULL get_fs_type() return even though
>the module was loaded... That is a corner case, there are other failures
>for request_module() though -- the other failures are not easy to
>reproduce though but fortunately we have a stress test driver to help
>with that now. Use the following tests:
>
> # tools/testing/selftests/kmod/kmod.sh -t 0008
> # tools/testing/selftests/kmod/kmod.sh -t 0009
>
>You can more easily see this error if you have kmod <= v19 installed.
>
>You will need to install kmod <= v19, be sure to install its modprobe
>into /sbin/ as by default the 'make install' target does not replace
>your own.
>
>This test helps cure test_kmod cases 0008 0009 so enable them.
>
>Reported-by: Martin Wilck <martin.wilck@suse.com>
>Reported-by: Randy Wright <rwright@hpe.com>
>Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Back from travel today, apologies for the delay. Will be able to give
this a proper look this week.
Jessica
next prev parent reply other threads:[~2017-01-04 2:54 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-08 18:47 [RFC 00/10] kmod: stress test driver, few fixes and enhancements Luis R. Rodriguez
2016-12-08 18:47 ` [RFC 01/10] kmod: add test driver to stress test the module loader Luis R. Rodriguez
2016-12-08 20:24 ` Kees Cook
2016-12-13 21:10 ` Luis R. Rodriguez
2016-12-16 7:41 ` Luis R. Rodriguez
2016-12-08 19:48 ` [RFC 02/10] module: fix memory leak on early load_module() failures Luis R. Rodriguez
2016-12-08 20:30 ` Kees Cook
2016-12-08 21:10 ` Luis R. Rodriguez
2016-12-08 21:17 ` Kees Cook
2016-12-09 17:06 ` Miroslav Benes
2016-12-16 8:51 ` Luis R. Rodriguez
2016-12-15 18:46 ` Aaron Tomlin
2016-12-08 19:48 ` [RFC 03/10] kmod: add dynamic max concurrent thread count Luis R. Rodriguez
2016-12-08 20:28 ` Kees Cook
2016-12-08 21:00 ` Luis R. Rodriguez
2016-12-14 15:38 ` Petr Mladek
2016-12-16 8:39 ` Luis R. Rodriguez
2017-01-10 19:24 ` Luis R. Rodriguez
2016-12-08 19:48 ` [RFC 04/10] kmod: provide wrappers for kmod_concurrent inc/dec Luis R. Rodriguez
2016-12-08 20:29 ` Kees Cook
2016-12-08 21:08 ` Luis R. Rodriguez
2016-12-15 12:46 ` Petr Mladek
2016-12-16 8:05 ` Luis R. Rodriguez
2016-12-22 4:48 ` Jessica Yu
2017-01-06 20:54 ` Luis R. Rodriguez
2017-01-10 18:57 ` [RFC 04/10] " Luis R. Rodriguez
2017-01-11 20:08 ` Luis R. Rodriguez
2017-05-16 18:02 ` Luis R. Rodriguez
2017-05-18 2:37 ` Luis R. Rodriguez
2016-12-22 5:07 ` Jessica Yu
2017-01-10 20:28 ` Luis R. Rodriguez
2016-12-08 19:48 ` [RFC 05/10] kmod: return -EBUSY if modprobe limit is reached Luis R. Rodriguez
2016-12-08 19:48 ` [RFC 06/10] kmod: provide sanity check on kmod_concurrent access Luis R. Rodriguez
2016-12-14 16:08 ` Petr Mladek
2016-12-14 17:12 ` Luis R. Rodriguez
2016-12-15 12:57 ` Petr Mladek
2017-01-10 20:00 ` Luis R. Rodriguez
2016-12-08 19:49 ` [RFC 07/10] kmod: use simplified rate limit printk Luis R. Rodriguez
2016-12-14 16:23 ` Petr Mladek
2016-12-14 16:41 ` Joe Perches
2016-12-16 8:44 ` Luis R. Rodriguez
2016-12-08 19:49 ` [RFC 08/10] sysctl: add support for unsigned int properly Luis R. Rodriguez
2016-12-08 19:49 ` [RFC 09/10] kmod: add helpers for getting kmod count and limit Luis R. Rodriguez
2016-12-15 16:56 ` Petr Mladek
2016-12-16 7:57 ` Luis R. Rodriguez
2017-01-11 18:27 ` Luis R. Rodriguez
2016-12-08 19:49 ` [RFC 10/10] kmod: add a sanity check on module loading Luis R. Rodriguez
2016-12-09 20:03 ` Martin Wilck
2016-12-09 20:56 ` Linus Torvalds
2016-12-15 18:08 ` Luis R. Rodriguez
2016-12-15 0:27 ` Rusty Russell
2016-12-16 8:31 ` Luis R. Rodriguez
2016-12-17 3:54 ` Rusty Russell
[not found] ` <CAB=NE6VvuA9a6hf6yoopGfUxVJQM5HyV5bNzUdsEtUV0UhbG-g@mail.gmail.com>
2016-12-20 0:53 ` Rusty Russell
2016-12-20 18:52 ` Luis R. Rodriguez
2016-12-21 2:21 ` Rusty Russell
2016-12-21 13:08 ` Luis R. Rodriguez
2017-01-03 0:04 ` Rusty Russell
2017-01-06 20:36 ` Luis R. Rodriguez
2017-01-06 21:53 ` Jessica Yu
2017-01-09 20:27 ` Luis R. Rodriguez
[not found] ` <87bmvgax51.fsf@rustcorp.com.au>
2017-01-09 19:56 ` [RFC 10/10] " Luis R. Rodriguez
2017-01-06 21:03 ` Jessica Yu
2017-01-04 2:47 ` Jessica Yu [this message]
2017-01-11 19:10 ` [RFC 00/10] kmod: stress test driver, few fixes and enhancements Luis R. Rodriguez
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