[PATCH] selftests: kmod: Add module address visibility test

[Kees Cook <keescook@chromium.org>]

Make sure we don't regress the CAP_SYSLOG behavior of the module address
visibility via /proc/modules nor /sys/module/*/sections/*.

Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
I forgot to include this patch in my kallsyms_show_value() f_cred series:
https://lore.kernel.org/lkml/20200702232638.2946421-1-keescook@chromium.org/
Since this depends on the changes, I'd like to include this in the
series with acks/review, etc. :)
---
 tools/testing/selftests/kmod/kmod.sh | 36 ++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/tools/testing/selftests/kmod/kmod.sh b/tools/testing/selftests/kmod/kmod.sh
index 3702dbcc90a7..c82aa77958e5 100755
--- a/tools/testing/selftests/kmod/kmod.sh
+++ b/tools/testing/selftests/kmod/kmod.sh
@@ -63,6 +63,8 @@ ALL_TESTS="$ALL_TESTS 0008:150:1"
 ALL_TESTS="$ALL_TESTS 0009:150:1"
 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"
 
 # Kselftest framework requirement - SKIP code is 4.
 ksft_skip=4
@@ -470,6 +472,38 @@ kmod_test_0011()
 	echo "$MODPROBE" > /proc/sys/kernel/modprobe
 }
 
+kmod_check_visibility()
+{
+	local name="$1"
+	local cmd="$2"
+
+	modprobe $DEFAULT_KMOD_DRIVER
+
+	local priv=$(eval $cmd)
+	local unpriv=$(capsh --drop=CAP_SYSLOG -- -c "$cmd")
+
+	if [ "$priv" = "$unpriv" ] || \
+	   [ "${priv:0:3}" = "0x0" ] || \
+	   [ "${unpriv:0:3}" != "0x0" ] ; then
+		echo "${FUNCNAME[0]}: FAIL, $name visible to unpriv: '$priv' vs '$unpriv'" >&2
+		exit 1
+	else
+		echo "${FUNCNAME[0]}: OK!"
+	fi
+}
+
+kmod_test_0012()
+{
+	kmod_check_visibility /proc/modules \
+		"grep '^${DEFAULT_KMOD_DRIVER}\b' /proc/modules | awk '{print \$NF}'"
+}
+
+kmod_test_0013()
+{
+	kmod_check_visibility '/sys/module/*/sections/*' \
+		"cat /sys/module/${DEFAULT_KMOD_DRIVER}/sections/.*text | head -n1"
+}
+
 list_tests()
 {
 	echo "Test ID list:"
@@ -489,6 +523,8 @@ list_tests()
 	echo "0009 x $(get_test_count 0009) - multithreaded - push kmod_concurrent over max_modprobes for get_fs_type()"
 	echo "0010 x $(get_test_count 0010) - test nonexistent modprobe path"
 	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"
 }
 
 usage()
-- 
2.25.1


-- 
Kees Cook