From 04f22107e1a2ead05401d9169fa4306e8c7eefad Mon Sep 17 00:00:00 2001 From: Peter Hutterer Date: Wed, 30 Mar 2022 09:25:22 +1000 Subject: evdev: strip the device name of format directives MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 (cherry picked from commit a423d7d3269dc32a87384f79e29bb5ac021c83d1) --- 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 d6b06cca..a909ff19 100644 --- a/meson.build +++ b/meson.build @@ -732,6 +732,7 @@ if get_option('tests') '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-pressurepad.c', 'test/litest-device-generic-singletouch.c', 'test/litest-device-gpio-keys.c', diff --git a/src/evdev.c b/src/evdev.c index d8dfdadd..0b4b3590 100644 --- a/src/evdev.c +++ b/src/evdev.c @@ -2291,19 +2291,19 @@ 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 @@ -2317,13 +2317,15 @@ 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); @@ -2346,6 +2348,9 @@ 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; @@ -2386,12 +2391,16 @@ evdev_device_create(struct libinput_seat *seat, return device; err: - close_restricted(libinput, fd); - if (device) { - unhandled_device = device->seat_caps == 0; - 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; } @@ -2404,7 +2413,7 @@ 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 * @@ -3001,6 +3010,8 @@ 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 @@ -43,6 +43,8 @@ #include #endif +#include "util-macros.h" + static inline bool streq(const char *str1, const char *str2) { @@ -398,3 +400,31 @@ safe_basename(const char *filename); char * trunkname(const char *filename); + +/** + * 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 b6ffbf4e..c16670e7 100644 --- a/test/litest.h +++ b/test/litest.h @@ -320,6 +320,7 @@ enum litest_device_type { LITEST_KEYBOARD_QUIRKED, LITEST_SYNAPTICS_PRESSUREPAD, LITEST_GENERIC_PRESSUREPAD, + 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 { @@ -1489,6 +1514,7 @@ litest_utils_suite(void) tcase_add_test(tc, strstrip_test); tcase_add_test(tc, strendswith_test); tcase_add_test(tc, strstartswith_test); + tcase_add_test(tc, strsanitize_test); tcase_add_test(tc, time_conversion); tcase_add_test(tc, human_time); -- cgit v1.2.1