From 2a8b8fde90d63d48ce09ddae44142674bbca1c28 Mon Sep 17 00:00:00 2001
From: Peter Hutterer <peter.hutterer@who-t.net>
Date: Wed, 30 Mar 2022 09:25:22 +1000
Subject: [PATCH] evdev: strip the device name of format directives
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This fixes a format string vulnerabilty.
evdev_log_message() composes a format string consisting of a fixed
prefix (including the rendered device name) and the passed-in format
buffer. This format string is then passed with the arguments to the
actual log handler, which usually and eventually ends up being printf.
If the device name contains a printf-style format directive, these ended
up in the format string and thus get interpreted correctly, e.g. for a
device "Foo%sBar" the log message vs printf invocation ends up being:
evdev_log_message(device, "some message %s", "some argument");
printf("event9 - Foo%sBar: some message %s", "some argument");
This can enable an attacker to execute malicious code with the
privileges of the process using libinput.
To exploit this, an attacker needs to be able to create a kernel device
with a malicious name, e.g. through /dev/uinput or a Bluetooth device.
To fix this, convert any potential format directives in the device name
by duplicating percentages.
Pre-rendering the device to avoid the issue altogether would be nicer
but the current log level hooks do not easily allow for this. The device
name is the only user-controlled part of the format string.
A second potential issue is the sysname of the device which is also
sanitized.
This issue was found by Albin Eldstål-Ahrens and Benjamin Svensson from
Assured AB, and independently by Lukas Lamster.
Fixes #752
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit a423d7d3269dc32a87384f79e29bb5ac021c83d1)
CVE: CVE-2022-1215
Upstream Status: Backport [https://gitlab.freedesktop.org/libinput/libinput/-/commit/2a8b8fde90d63d48ce09ddae44142674bbca1c28]
Signed-off-by: Pawan Badganchi <Pawan.Badganchi@kpit.com>
---
meson.build | 1 +
src/evdev.c | 31 +++++++++++------
src/evdev.h | 6 ++--
src/util-strings.h | 30 ++++++++++++++++
test/litest-device-format-string.c | 56 ++++++++++++++++++++++++++++++
test/litest.h | 1 +
test/test-utils.c | 26 ++++++++++++++
7 files changed, 139 insertions(+), 12 deletions(-)
create mode 100644 test/litest-device-format-string.c
diff --git a/meson.build b/meson.build
index 90f528e6..1f6159e7 100644
--- a/meson.build
+++ b/meson.build
@@ -787,6 +787,7 @@
'test/litest-device-dell-canvas-totem-touch.c',
'test/litest-device-elantech-touchpad.c',
'test/litest-device-elan-tablet.c',
+ 'test/litest-device-format-string.c',
'test/litest-device-generic-singletouch.c',
'test/litest-device-gpio-keys.c',
'test/litest-device-huion-pentablet.c',
diff --git a/src/evdev.c b/src/evdev.c
index 6d81f58f..d1c35c07 100644
--- a/src/evdev.c
+++ b/src/evdev.c
@@ -2356,19 +2356,19 @@ evdev_device_create(struct libinput_seat *seat,
struct libinput *libinput = seat->libinput;
struct evdev_device *device = NULL;
int rc;
- int fd;
+ int fd = -1;
int unhandled_device = 0;
const char *devnode = udev_device_get_devnode(udev_device);
- const char *sysname = udev_device_get_sysname(udev_device);
+ char *sysname = str_sanitize(udev_device_get_sysname(udev_device));
if (!devnode) {
log_info(libinput, "%s: no device node associated\n", sysname);
- return NULL;
+ goto err;
}
if (udev_device_should_be_ignored(udev_device)) {
log_debug(libinput, "%s: device is ignored\n", sysname);
- return NULL;
+ goto err;
}
/* Use non-blocking mode so that we can loop on read on
@@ -2382,13 +2382,15 @@ evdev_device_create(struct libinput_seat *seat,
sysname,
devnode,
strerror(-fd));
- return NULL;
+ goto err;
}
if (!evdev_device_have_same_syspath(udev_device, fd))
goto err;
device = zalloc(sizeof *device);
+ device->sysname = sysname;
+ sysname = NULL;
libinput_device_init(&device->base, seat);
libinput_seat_ref(seat);
@@ -2411,6 +2413,9 @@ evdev_device_create(struct libinput_seat *seat,
device->dispatch = NULL;
device->fd = fd;
device->devname = libevdev_get_name(device->evdev);
+ /* the log_prefix_name is used as part of a printf format string and
+ * must not contain % directives, see evdev_log_msg */
+ device->log_prefix_name = str_sanitize(device->devname);
device->scroll.threshold = 5.0; /* Default may be overridden */
device->scroll.direction_lock_threshold = 5.0; /* Default may be overridden */
device->scroll.direction = 0;
@@ -2238,9 +2238,14 @@
return device;
err:
- close_restricted(libinput, fd);
- if (device)
- evdev_device_destroy(device);
+ if (fd >= 0) {
+ close_restricted(libinput, fd);
+ if (device) {
+ unhandled_device = device->seat_caps == 0;
+ evdev_device_destroy(device);
+ }
+ }
+ free(sysname);
return unhandled_device ? EVDEV_UNHANDLED_DEVICE : NULL;
}
@@ -2469,7 +2478,7 @@ evdev_device_get_output(struct evdev_device *device)
const char *
evdev_device_get_sysname(struct evdev_device *device)
{
- return udev_device_get_sysname(device->udev_device);
+ return device->sysname;
}
const char *
@@ -3066,6 +3075,8 @@ evdev_device_destroy(struct evdev_device *device)
if (device->base.group)
libinput_device_group_unref(device->base.group);
+ free(device->log_prefix_name);
+ free(device->sysname);
free(device->output_name);
filter_destroy(device->pointer.filter);
libinput_timer_destroy(&device->scroll.timer);
diff --git a/src/evdev.h b/src/evdev.h
index c7d130f8..980c5943 100644
--- a/src/evdev.h
+++ b/src/evdev.h
@@ -169,6 +169,8 @@ struct evdev_device {
struct udev_device *udev_device;
char *output_name;
const char *devname;
+ char *log_prefix_name;
+ char *sysname;
bool was_removed;
int fd;
enum evdev_device_seat_capability seat_caps;
@@ -786,7 +788,7 @@ evdev_log_msg(struct evdev_device *device,
sizeof(buf),
"%-7s - %s%s%s",
evdev_device_get_sysname(device),
- (priority > LIBINPUT_LOG_PRIORITY_DEBUG) ? device->devname : "",
+ (priority > LIBINPUT_LOG_PRIORITY_DEBUG) ? device->log_prefix_name : "",
(priority > LIBINPUT_LOG_PRIORITY_DEBUG) ? ": " : "",
format);
@@ -824,7 +826,7 @@ evdev_log_msg_ratelimit(struct evdev_device *device,
sizeof(buf),
"%-7s - %s%s%s",
evdev_device_get_sysname(device),
- (priority > LIBINPUT_LOG_PRIORITY_DEBUG) ? device->devname : "",
+ (priority > LIBINPUT_LOG_PRIORITY_DEBUG) ? device->log_prefix_name : "",
(priority > LIBINPUT_LOG_PRIORITY_DEBUG) ? ": " : "",
format);
diff --git a/src/util-strings.h b/src/util-strings.h
index 2a15fab3..d5a84146 100644
--- a/src/util-strings.h
+++ b/src/util-strings.h
@@ -42,6 +42,7 @@
#ifdef HAVE_XLOCALE_H
#include <xlocale.h>
#endif
+#include "util-macros.h"
#define streq(s1, s2) (strcmp((s1), (s2)) == 0)
#define strneq(s1, s2, n) (strncmp((s1), (s2), (n)) == 0)
@@ -312,3 +313,31 @@
free(result);
return -1;
}
+
+/**
+ * Return a copy of str with all % converted to %% to make the string
+ * acceptable as printf format.
+ */
+static inline char *
+str_sanitize(const char *str)
+{
+ if (!str)
+ return NULL;
+
+ if (!strchr(str, '%'))
+ return strdup(str);
+
+ size_t slen = min(strlen(str), 512);
+ char *sanitized = zalloc(2 * slen + 1);
+ const char *src = str;
+ char *dst = sanitized;
+
+ for (size_t i = 0; i < slen; i++) {
+ if (*src == '%')
+ *dst++ = '%';
+ *dst++ = *src++;
+ }
+ *dst = '\0';
+
+ return sanitized;
+}
diff --git a/test/litest-device-format-string.c b/test/litest-device-format-string.c
new file mode 100644
index 00000000..aed15db4
--- /dev/null
+++ b/test/litest-device-format-string.c
@@ -0,0 +1,56 @@
+
+/*
+ * Copyright © 2013 Red Hat, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include "config.h"
+
+#include "litest.h"
+#include "litest-int.h"
+
+static struct input_id input_id = {
+ .bustype = 0x3,
+ .vendor = 0x0123,
+ .product = 0x0456,
+};
+
+static int events[] = {
+ EV_KEY, BTN_LEFT,
+ EV_KEY, BTN_RIGHT,
+ EV_KEY, BTN_MIDDLE,
+ EV_REL, REL_X,
+ EV_REL, REL_Y,
+ EV_REL, REL_WHEEL,
+ EV_REL, REL_WHEEL_HI_RES,
+ -1 , -1,
+};
+
+TEST_DEVICE("mouse-format-string",
+ .type = LITEST_MOUSE_FORMAT_STRING,
+ .features = LITEST_RELATIVE | LITEST_BUTTON | LITEST_WHEEL,
+ .interface = NULL,
+
+ .name = "Evil %s %d %x Mouse %p %",
+ .id = &input_id,
+ .absinfo = NULL,
+ .events = events,
+)
diff --git a/test/litest.h b/test/litest.h
index 4982e516..1b1daa90 100644
--- a/test/litest.h
+++ b/test/litest.h
@@ -303,6 +303,7 @@
LITEST_ALPS_3FG,
LITEST_ELAN_TABLET,
LITEST_ABSINFO_OVERRIDE,
+ LITEST_MOUSE_FORMAT_STRING,
};
#define LITEST_DEVICELESS -2
diff --git a/test/test-utils.c b/test/test-utils.c
index 989adecd..e80754be 100644
--- a/test/test-utils.c
+++ b/test/test-utils.c
@@ -1267,6 +1267,31 @@ START_TEST(strstartswith_test)
}
END_TEST
+START_TEST(strsanitize_test)
+{
+ struct strsanitize_test {
+ const char *string;
+ const char *expected;
+ } tests[] = {
+ { "foobar", "foobar" },
+ { "", "" },
+ { "%", "%%" },
+ { "%%%%", "%%%%%%%%" },
+ { "x %s", "x %%s" },
+ { "x %", "x %%" },
+ { "%sx", "%%sx" },
+ { "%s%s", "%%s%%s" },
+ { NULL, NULL },
+ };
+
+ for (struct strsanitize_test *t = tests; t->string; t++) {
+ char *sanitized = str_sanitize(t->string);
+ ck_assert_str_eq(sanitized, t->expected);
+ free(sanitized);
+ }
+}
+END_TEST
+
START_TEST(list_test_insert)
{
struct list_test {
@@ -1138,6 +1138,7 @@
tcase_add_test(tc, strsplit_test);
tcase_add_test(tc, kvsplit_double_test);
tcase_add_test(tc, strjoin_test);
+ tcase_add_test(tc, strsanitize_test);
tcase_add_test(tc, time_conversion);
tcase_add_test(tc, list_test_insert);
--
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