linux-kernel - Re: request

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Date:   Sun, 8 May 2022 18:42:28 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...abs.org>,
        "fnovak@...ibm.com" <fnovak@...ibm.com>
Subject: Re: request_module DoS

On Sat, May 07, 2022 at 12:14:47PM -0700, Luis Chamberlain wrote:
> On Sat, May 07, 2022 at 01:02:20AM -0700, Luis Chamberlain wrote:
> > You can try to reproduce by using adding a new test type for crypto-aegis256
> > on lib/test_kmod.c. These tests however can try something similar but other
> > modules.
> > 
> > /tools/testing/selftests/kmod/kmod.sh -t 0008
> > /tools/testing/selftests/kmod/kmod.sh -t 0009
> > 
> > I can't decipher this yet.
> 
> Without testing it... but something like this might be an easier
> reproducer:
> 
> +	config_set_driver crypto-aegis256

If the module is not present though nothing really happens, and so
is it possible this is another issue?

Below a bogus module request.

diff --git a/tools/testing/selftests/kmod/kmod.sh b/tools/testing/selftests/kmod/kmod.sh
index afd42387e8b2..a747ad549940 100755
--- a/tools/testing/selftests/kmod/kmod.sh
+++ b/tools/testing/selftests/kmod/kmod.sh
@@ -65,6 +66,7 @@ ALL_TESTS="$ALL_TESTS 0010:1:1"
 ALL_TESTS="$ALL_TESTS 0011:1:1"
 ALL_TESTS="$ALL_TESTS 0012:1:1"
 ALL_TESTS="$ALL_TESTS 0013:1:1"
+ALL_TESTS="$ALL_TESTS 0014:150:1"
 
 # Kselftest framework requirement - SKIP code is 4.
 ksft_skip=4
@@ -504,6 +506,17 @@ kmod_test_0013()
 		"cat /sys/module/${DEFAULT_KMOD_DRIVER}/sections/.*text | head -n1"
 }
 
+kmod_test_0014()
+{
+	kmod_defaults_driver
+	MODPROBE_LIMIT=$(config_get_modprobe_limit)
+	let EXTRA=$MODPROBE_LIMIT/6
+	config_set_driver bogus_module_does_not_exist
+	config_num_thread_limit_extra $EXTRA
+	config_trigger ${FUNCNAME[0]}
+	config_expect_result ${FUNCNAME[0]} MODULE_NOT_FOUND
+}
+
 list_tests()
 {
 	echo "Test ID list:"
@@ -525,6 +538,7 @@ list_tests()
 	echo "0011 x $(get_test_count 0011) - test completely disabling module autoloading"
 	echo "0012 x $(get_test_count 0012) - test /proc/modules address visibility under CAP_SYSLOG"
 	echo "0013 x $(get_test_count 0013) - test /sys/module/*/sections/* visibility under CAP_SYSLOG"
+	echo "0014 x $(get_test_count 0014) - multithreaded - push kmod_concurrent over max_modprobes for request_module() for a missing module"
 }
 
 usage()