[PATCH net-next v3 2/2] selftests: ptp: add a regression test for the frequency adjustment overflow

[Deep Shah <deepshah146@gmail.com>]

testptp's -f option stores the requested adjustment as an int ppb and
converts it to scaled ppm, so it cannot express the 64-bit scaled-ppm
values needed to overflow scaled_ppm_to_ppb() and bypass the max_adj
check enforced by ptp_clock_adjtime().

Add a small test that crafts struct timex.freq directly and verifies that
an overflowing frequency adjustment is rejected with -ERANGE.  The test
skips when no frequency-adjustable PTP device is available.

Signed-off-by: Deep Shah <deepshah146@gmail.com>
---
 tools/testing/selftests/ptp/.gitignore        |   1 +
 tools/testing/selftests/ptp/Makefile          |   2 +-
 .../testing/selftests/ptp/ptp_freq_overflow.c | 101 ++++++++++++++++++
 3 files changed, 103 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/ptp/ptp_freq_overflow.c

diff --git a/tools/testing/selftests/ptp/.gitignore b/tools/testing/selftests/ptp/.gitignore
index 534ca26eee48..e63194b44395 100644
--- a/tools/testing/selftests/ptp/.gitignore
+++ b/tools/testing/selftests/ptp/.gitignore
@@ -1,2 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0-only
 testptp
+ptp_freq_overflow
diff --git a/tools/testing/selftests/ptp/Makefile b/tools/testing/selftests/ptp/Makefile
index 8f57f88ecadd..dd7376cc9bf5 100644
--- a/tools/testing/selftests/ptp/Makefile
+++ b/tools/testing/selftests/ptp/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 CFLAGS += $(KHDR_INCLUDES)
-TEST_GEN_PROGS := testptp
+TEST_GEN_PROGS := testptp ptp_freq_overflow
 LDLIBS += -lrt
 TEST_PROGS = phc.sh
 
diff --git a/tools/testing/selftests/ptp/ptp_freq_overflow.c b/tools/testing/selftests/ptp/ptp_freq_overflow.c
new file mode 100644
index 000000000000..e90477175958
--- /dev/null
+++ b/tools/testing/selftests/ptp/ptp_freq_overflow.c
@@ -0,0 +1,101 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Regression test for the scaled_ppm_to_ppb() integer overflow that allowed
+ * a crafted clock_adjtime(ADJ_FREQUENCY) to bypass the PTP max_adj check.
+ *
+ * testptp's -f option stores the adjustment as an int ppb and cannot express
+ * the 64-bit scaled-ppm values needed to overflow the conversion, so this
+ * test crafts struct timex.freq directly.
+ */
+#define _GNU_SOURCE
+#define __SANE_USERSPACE_TYPES__
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/timex.h>
+#include <time.h>
+#include <unistd.h>
+#include <linux/ptp_clock.h>
+#include "../kselftest.h"
+
+#define FD_TO_CLOCKID(fd)	((clockid_t)((((unsigned int)~(fd)) << 3) | 3))
+
+/* clock_adjtime is not available in GLIBC < 2.14 */
+#if !__GLIBC_PREREQ(2, 14)
+#include <sys/syscall.h>
+static int clock_adjtime(clockid_t id, struct timex *tx)
+{
+	return syscall(__NR_clock_adjtime, id, tx);
+}
+#endif
+
+int main(int argc, char *argv[])
+{
+	const char *device = argc > 1 ? argv[1] : "/dev/ptp0";
+	struct ptp_clock_caps caps;
+	struct timex restore = { 0 };
+	struct timex tx = { 0 };
+	clockid_t clkid;
+	int fd, ret;
+
+	ksft_print_header();
+	ksft_set_plan(1);
+
+	if (sizeof(tx.freq) < 8)
+		ksft_exit_skip("the overflow only affects 64-bit kernels\n");
+
+	fd = open(device, O_RDWR);
+	if (fd < 0)
+		ksft_exit_skip("cannot open %s: %s\n", device, strerror(errno));
+
+	clkid = FD_TO_CLOCKID(fd);
+
+	if (ioctl(fd, PTP_CLOCK_GETCAPS, &caps))
+		ksft_exit_skip("PTP_CLOCK_GETCAPS on %s: %s\n", device, strerror(errno));
+	if (!caps.max_adj)
+		ksft_exit_skip("%s does not support frequency adjustment\n", device);
+
+	/*
+	 * Remember the current frequency.  A vulnerable kernel accepts the
+	 * bogus value below and programs it into the hardware, so restore the
+	 * original afterwards instead of leaving the clock corrupted.
+	 */
+	if (clock_adjtime(clkid, &restore))
+		ksft_exit_skip("clock_adjtime(get) on %s: %s\n", device, strerror(errno));
+	restore.modes = ADJ_FREQUENCY;
+
+	/*
+	 * (1 + 147573952589676412) * 125 == 2^64 + 9, which overflows s64 in
+	 * scaled_ppm_to_ppb() and wraps the result to a ppb of 0.  A kernel
+	 * that does not detect the overflow lets this absurd frequency past
+	 * the max_adj check; a fixed kernel rejects it with -ERANGE.
+	 *
+	 * The cast avoids a -Woverflow warning where tx.freq is 32-bit
+	 * without tying the value to the width of long, which differs from
+	 * the width of tx.freq on x32 and other y2038 configurations.
+	 */
+	tx.modes = ADJ_FREQUENCY;
+	tx.freq = (__typeof__(tx.freq))147573952589676412LL;
+
+	ret = clock_adjtime(clkid, &tx);
+	if (ret < 0 && errno == EBUSY) {
+		/*
+		 * A free-running physical clock (virtual clocks active) rejects
+		 * frequency adjustment with -EBUSY before the overflow is even
+		 * evaluated, so the test cannot run here.
+		 */
+		ksft_test_result_skip("%s: frequency adjustment returned EBUSY, skipping\n",
+				      device);
+	} else {
+		ksft_test_result(ret < 0 && errno == ERANGE,
+				 "overflowing frequency adjustment is rejected (ret=%d errno=%d)\n",
+				 ret, ret < 0 ? errno : 0);
+	}
+
+	/* put the frequency back the way we found it */
+	clock_adjtime(clkid, &restore);
+
+	close(fd);
+	ksft_finished();
+}
-- 
2.43.0