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From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Filipe Manana <fdmanana@suse.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	rgoldwyn@suse.com, hare <hare@suse.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-kselftest@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Aaron Tomlin <atomlin@redhat.com>,
	rwright@hpe.com, Heinrich Schuchardt <xypron.glpk@gmx.de>,
	Michal Marek <mmarek@suse.com>,
	martin.wilck@suse.com, Jeff Mahoney <jeffm@suse.com>,
	Ingo Molnar <mingo@redhat.com>, Petr Mladek <pmladek@suse.com>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Guenter Roeck <linux@roeck-us.net>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	shuah@kernel.org, DSterba@suse.com,
	Kees Cook <keescook@chromium.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Miroslav Benes <mbenes@suse.cz>, NeilBrown <neilb@suse.com>,
	"linux-kernel@vger.kernel.o rg" <linux-kernel@vger.kernel.org>,
	David Miller <davem@davemloft.net>, Jessica Yu <jeyu@redhat.com>,
	Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>,
	Julia Lawall <julia.lawall@lip6.fr>
Subject: Re: [RFC 10/10] kmod: add a sanity check on module loading
Date: Wed, 21 Dec 2016 07:08:25 -0600	[thread overview]
Message-ID: <CAB=NE6Wd4jvUVS6pNds0yND_PX-MMpVjtvnJOHsNWX_5H7Mdkg@mail.gmail.com> (raw)
In-Reply-To: <87a8bqja3i.fsf@rustcorp.com.au>

On Tue, Dec 20, 2016 at 8:21 PM, Rusty Russell <rusty@rustcorp.com.au> wrote:
> "Luis R. Rodriguez" <mcgrof@kernel.org> writes:
>> OK -- if userspace messes up again it may be a bit hard to prove
>> unless we have a validation debug thing in place, would such a thing
>> in debug form be reasonable ?
>
> That makes perfect sense.  Untested hack:
>
> diff --git a/fs/filesystems.c b/fs/filesystems.c
> index c5618db110be..e5c90e80c7d3 100644
> --- a/fs/filesystems.c
> +++ b/fs/filesystems.c
> @@ -275,9 +275,10 @@ struct file_system_type *get_fs_type(const char *name)
>         int len = dot ? dot - name : strlen(name);
>
>         fs = __get_fs_type(name, len);
> -       if (!fs && (request_module("fs-%.*s", len, name) == 0))
> +       if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
>                 fs = __get_fs_type(name, len);
> -
> +               WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
> +       }
>         if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
>                 put_filesystem(fs);
>                 fs = NULL;

This is precisely a type of debug patch we had added first to verify "WTF".

> Maybe a similar hack for try_then_request_module(), but many places seem
> to open-code request_module() so it's not as trivial...

Right, out of ~350 request_module() calls (not included try requests)
only ~46 check the return value. Hence a validation check, and come to
think of it, *this* was the issue that originally had me believing
that in some places we might end up in a null deref --if those open
coded request_module() calls assume the driver is loaded there could
be many places where a NULL is inevitable. Granted, I agree they
should be fixed, we could add a grammar rule to start nagging at
driver developers for started, but it does beg the question also of
what a tightly knit validation for modprobe might look like, and hence
this patch and now the completed not-yet-posted alias work.

Would it be worthy as a kconfig kmod debugging aide for now? I can
follow up with a semantic patch to nag about checking the return value
of request_module(), and we can  have 0-day then also complain about
new invalid uses.

  Luis

  reply	other threads:[~2016-12-21 13:08 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 [this message]
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
2017-01-11 19:10 ` [RFC 00/10] kmod: stress test driver, few fixes and enhancements Luis R. Rodriguez

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