linux-kernel - Re: [RFC 10/10] kmod: add a sanity check on module loading

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Date:   Wed, 21 Dec 2016 12:51:21 +1030
From:   Rusty Russell <rusty@...tcorp.com.au>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Filipe Manana <fdmanana@...e.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        "linux-doc\@vger.kernel.org" <linux-doc@...r.kernel.org>,
        rgoldwyn@...e.com, hare <hare@...e.com>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Aaron Tomlin <atomlin@...hat.com>, rwright@....com,
        Heinrich Schuchardt <xypron.glpk@....de>,
        Michal Marek <mmarek@...e.com>, martin.wilck@...e.com,
        Jeff Mahoney <jeffm@...e.com>, Ingo Molnar <mingo@...hat.com>,
        Petr Mladek <pmladek@...e.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, shuah@...nel.org,
        DSterba@...e.com, Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>, NeilBrown <neilb@...e.com>,
        "linux-kernel\@vger.kernel.o rg" <linux-kernel@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jessica Yu <jeyu@...hat.com>,
        Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
        Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [RFC 10/10] kmod: add a sanity check on module loading

"Luis R. Rodriguez" <mcgrof@...nel.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;

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

Cheers,
Rusty.