tools/testing/selftests/sysctl: validate sysctl_writes_strict

This adds several behavioral tests to sysctl string and number writing
to detect unexpected cases that behaved differently when the sysctl
kernel.sysctl_writes_strict != 1.

[ original ]
root@localhost:~# make test_num
== Testing sysctl behavior against /proc/sys/kernel/domainname ==
Writing test file ... ok
Checking sysctl is not set to test value ... ok
Writing sysctl from shell ... ok
Resetting sysctl to original value ... ok
Writing entire sysctl in single write ... ok
Writing middle of sysctl after synchronized seek ... FAIL
Writing beyond end of sysctl ... FAIL
Writing sysctl with multiple long writes ... FAIL
Writing entire sysctl in short writes ... FAIL
Writing middle of sysctl after unsynchronized seek ... ok
Checking sysctl maxlen is at least 65 ... ok
Checking sysctl keeps original string on overflow append ... FAIL
Checking sysctl stays NULL terminated on write ... ok
Checking sysctl stays NULL terminated on overwrite ... ok
make: *** [test_num] Error 1
root@localhost:~# make test_string
== Testing sysctl behavior against /proc/sys/vm/swappiness ==
Writing test file ... ok
Checking sysctl is not set to test value ... ok
Writing sysctl from shell ... ok
Resetting sysctl to original value ... ok
Writing entire sysctl in single write ... ok
Writing middle of sysctl after synchronized seek ... FAIL
Writing beyond end of sysctl ... FAIL
Writing sysctl with multiple long writes ... ok
make: *** [test_string] Error 1

[ with CONFIG_PROC_SYSCTL_STRICT_WRITES ]
root@localhost:~# make run_tests
== Testing sysctl behavior against /proc/sys/kernel/domainname ==
Writing test file ... ok
Checking sysctl is not set to test value ... ok
Writing sysctl from shell ... ok
Resetting sysctl to original value ... ok
Writing entire sysctl in single write ... ok
Writing middle of sysctl after synchronized seek ... ok
Writing beyond end of sysctl ... ok
Writing sysctl with multiple long writes ... ok
Writing entire sysctl in short writes ... ok
Writing middle of sysctl after unsynchronized seek ... ok
Checking sysctl maxlen is at least 65 ... ok
Checking sysctl keeps original string on overflow append ... ok
Checking sysctl stays NULL terminated on write ... ok
Checking sysctl stays NULL terminated on overwrite ... ok
== Testing sysctl behavior against /proc/sys/vm/swappiness ==
Writing test file ... ok
Checking sysctl is not set to test value ... ok
Writing sysctl from shell ... ok
Resetting sysctl to original value ... ok
Writing entire sysctl in single write ... ok
Writing middle of sysctl after synchronized seek ... ok
Writing beyond end of sysctl ... ok
Writing sysctl with multiple long writes ... ok

Signed-off-by: Kees Cook <[e-mail]>
Cc: Randy Dunlap <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

tools/testing/selftests/Makefile

···
 TARGETS += vm
 TARGETS += powerpc
 TARGETS += user
+TARGETS += sysctl
 
 all:
 	for TARGET in $(TARGETS); do \

tools/testing/selftests/sysctl/Makefile

···
+# Makefile for sysctl selftests.
+# Expects kernel.sysctl_writes_strict=1.
+
+# No binaries, but make sure arg-less "make" doesn't trigger "run_tests".
+all:
+
+# Allow specific tests to be selected.
+test_num:
+	@/bin/sh ./run_numerictests
+
+test_string:
+	@/bin/sh ./run_stringtests
+
+run_tests: all test_num test_string
+
+# Nothing to clean up.
+clean:
+
+.PHONY: all run_tests clean test_num test_string

tools/testing/selftests/sysctl/common_tests

···
+#!/bin/sh
+
+TEST_FILE=$(mktemp)
+
+echo "== Testing sysctl behavior against ${TARGET} =="
+
+set_orig()
+{
+	echo "${ORIG}" > "${TARGET}"
+}
+
+set_test()
+{
+	echo "${TEST_STR}" > "${TARGET}"
+}
+
+verify()
+{
+	local seen
+	seen=$(cat "$1")
+	if [ "${seen}" != "${TEST_STR}" ]; then
+		return 1
+	fi
+	return 0
+}
+
+trap 'set_orig; rm -f "${TEST_FILE}"' EXIT
+
+rc=0
+
+echo -n "Writing test file ... "
+echo "${TEST_STR}" > "${TEST_FILE}"
+if ! verify "${TEST_FILE}"; then
+	echo "FAIL" >&2
+	exit 1
+else
+	echo "ok"
+fi
+
+echo -n "Checking sysctl is not set to test value ... "
+if verify "${TARGET}"; then
+	echo "FAIL" >&2
+	exit 1
+else
+	echo "ok"
+fi
+
+echo -n "Writing sysctl from shell ... "
+set_test
+if ! verify "${TARGET}"; then
+	echo "FAIL" >&2
+	exit 1
+else
+	echo "ok"
+fi
+
+echo -n "Resetting sysctl to original value ... "
+set_orig
+if verify "${TARGET}"; then
+	echo "FAIL" >&2
+	exit 1
+else
+	echo "ok"
+fi
+
+# Now that we've validated the sanity of "set_test" and "set_orig",
+# we can use those functions to set starting states before running
+# specific behavioral tests.
+
+echo -n "Writing entire sysctl in single write ... "
+set_orig
+dd if="${TEST_FILE}" of="${TARGET}" bs=4096 2>/dev/null
+if ! verify "${TARGET}"; then
+	echo "FAIL" >&2
+	rc=1
+else
+	echo "ok"
+fi
+
+echo -n "Writing middle of sysctl after synchronized seek ... "
+set_test
+dd if="${TEST_FILE}" of="${TARGET}" bs=1 seek=1 skip=1 2>/dev/null
+if ! verify "${TARGET}"; then
+	echo "FAIL" >&2
+	rc=1
+else
+	echo "ok"
+fi
+
+echo -n "Writing beyond end of sysctl ... "
+set_orig
+dd if="${TEST_FILE}" of="${TARGET}" bs=20 seek=2 2>/dev/null
+if verify "${TARGET}"; then
+        echo "FAIL" >&2
+        rc=1
+else
+        echo "ok"
+fi
+
+echo -n "Writing sysctl with multiple long writes ... "
+set_orig
+(perl -e 'print "A" x 50;'; echo "${TEST_STR}") | \
+	dd of="${TARGET}" bs=50 2>/dev/null
+if verify "${TARGET}"; then
+	echo "FAIL" >&2
+	rc=1
+else
+	echo "ok"
+fi

tools/testing/selftests/sysctl/run_numerictests

···
+#!/bin/sh
+
+SYSCTL="/proc/sys"
+TARGET="${SYSCTL}/vm/swappiness"
+ORIG=$(cat "${TARGET}")
+TEST_STR=$(( $ORIG + 1 ))
+
+. ./common_tests
+
+exit $rc

tools/testing/selftests/sysctl/run_stringtests

···
+#!/bin/sh
+
+SYSCTL="/proc/sys"
+TARGET="${SYSCTL}/kernel/domainname"
+ORIG=$(cat "${TARGET}")
+TEST_STR="Testing sysctl"
+
+. ./common_tests
+
+# Only string sysctls support seeking/appending.
+MAXLEN=65
+
+echo -n "Writing entire sysctl in short writes ... "
+set_orig
+dd if="${TEST_FILE}" of="${TARGET}" bs=1 2>/dev/null
+if ! verify "${TARGET}"; then
+	echo "FAIL" >&2
+	rc=1
+else
+	echo "ok"
+fi
+
+echo -n "Writing middle of sysctl after unsynchronized seek ... "
+set_test
+dd if="${TEST_FILE}" of="${TARGET}" bs=1 seek=1 2>/dev/null
+if verify "${TARGET}"; then
+	echo "FAIL" >&2
+	rc=1
+else
+	echo "ok"
+fi
+
+echo -n "Checking sysctl maxlen is at least $MAXLEN ... "
+set_orig
+perl -e 'print "A" x ('"${MAXLEN}"'-2), "B";' | \
+	dd of="${TARGET}" bs="${MAXLEN}" 2>/dev/null
+if ! grep -q B "${TARGET}"; then
+	echo "FAIL" >&2
+	rc=1
+else
+	echo "ok"
+fi
+
+echo -n "Checking sysctl keeps original string on overflow append ... "
+set_orig
+perl -e 'print "A" x ('"${MAXLEN}"'-1), "B";' | \
+	dd of="${TARGET}" bs=$(( MAXLEN - 1 )) 2>/dev/null
+if grep -q B "${TARGET}"; then
+	echo "FAIL" >&2
+	rc=1
+else
+	echo "ok"
+fi
+
+echo -n "Checking sysctl stays NULL terminated on write ... "
+set_orig
+perl -e 'print "A" x ('"${MAXLEN}"'-1), "B";' | \
+	dd of="${TARGET}" bs="${MAXLEN}" 2>/dev/null
+if grep -q B "${TARGET}"; then
+	echo "FAIL" >&2
+	rc=1
+else
+	echo "ok"
+fi
+
+echo -n "Checking sysctl stays NULL terminated on overwrite ... "
+set_orig
+perl -e 'print "A" x ('"${MAXLEN}"'-1), "BB";' | \
+	dd of="${TARGET}" bs=$(( $MAXLEN + 1 )) 2>/dev/null
+if grep -q B "${TARGET}"; then
+	echo "FAIL" >&2
+	rc=1
+else
+	echo "ok"
+fi
+
+exit $rc