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From: Martin Pitt <martin@piware.de>
Date: Sun, 17 Feb 2019 10:17:45 +0100
Subject: sd-bus: enforce a size limit on D-Bus object paths
Replace stack with heap allocation. This avoids accessing/modifying
memory outside of the allocated stack region by sending specially
crafted D-Bus messages with very large object paths.
Vulnerability discovered by Chris Coulson <chris.coulson@canonical.com>,
patch provided by Riccardo Schirone <rschiron@redhat.com>.
CVE-2019-6454
---
src/libsystemd/sd-bus/bus-internal.c | 2 +-
src/libsystemd/sd-bus/bus-internal.h | 4 +++
src/libsystemd/sd-bus/bus-objects.c | 64 ++++++++++++++++++++++++++++--------
3 files changed, 55 insertions(+), 15 deletions(-)
diff --git a/src/libsystemd/sd-bus/bus-internal.c b/src/libsystemd/sd-bus/bus-internal.c
index 40acae2..598b7f1 100644
--- a/src/libsystemd/sd-bus/bus-internal.c
+++ b/src/libsystemd/sd-bus/bus-internal.c
@@ -43,7 +43,7 @@ bool object_path_is_valid(const char *p) {
if (slash)
return false;
- return true;
+ return (q - p) <= BUS_PATH_SIZE_MAX;
}
char* object_path_startswith(const char *a, const char *b) {
diff --git a/src/libsystemd/sd-bus/bus-internal.h b/src/libsystemd/sd-bus/bus-internal.h
index f208b29..a8d61bf 100644
--- a/src/libsystemd/sd-bus/bus-internal.h
+++ b/src/libsystemd/sd-bus/bus-internal.h
@@ -332,6 +332,10 @@ struct sd_bus {
#define BUS_MESSAGE_SIZE_MAX (128*1024*1024)
#define BUS_AUTH_SIZE_MAX (64*1024)
+/* Note that the D-Bus specification states that bus paths shall have no size limit. We enforce here one
+ * anyway, since truly unbounded strings are a security problem. The limit we pick is relatively large however,
+ * to not clash unnecessarily with real-life applications. */
+#define BUS_PATH_SIZE_MAX (64*1024)
#define BUS_CONTAINER_DEPTH 128
diff --git a/src/libsystemd/sd-bus/bus-objects.c b/src/libsystemd/sd-bus/bus-objects.c
index 58329f3..983921d 100644
--- a/src/libsystemd/sd-bus/bus-objects.c
+++ b/src/libsystemd/sd-bus/bus-objects.c
@@ -1133,7 +1133,8 @@ static int object_manager_serialize_path_and_fallbacks(
const char *path,
sd_bus_error *error) {
- char *prefix;
+ _cleanup_free_ char *prefix = NULL;
+ size_t pl;
int r;
assert(bus);
@@ -1149,7 +1150,11 @@ static int object_manager_serialize_path_and_fallbacks(
return 0;
/* Second, add fallback vtables registered for any of the prefixes */
- prefix = newa(char, strlen(path) + 1);
+ pl = strlen(path);
+ assert(pl <= BUS_PATH_SIZE_MAX);
+ prefix = new(char, pl + 1);
+ if (!prefix)
+ return -ENOMEM;
OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
r = object_manager_serialize_path(bus, reply, prefix, path, true, error);
if (r < 0)
@@ -1345,6 +1350,7 @@ static int object_find_and_run(
}
int bus_process_object(sd_bus *bus, sd_bus_message *m) {
+ _cleanup_free_ char *prefix = NULL;
int r;
size_t pl;
bool found_object = false;
@@ -1369,9 +1375,12 @@ int bus_process_object(sd_bus *bus, sd_bus_message *m) {
assert(m->member);
pl = strlen(m->path);
- do {
- char prefix[pl+1];
+ assert(pl <= BUS_PATH_SIZE_MAX);
+ prefix = new(char, pl + 1);
+ if (!prefix)
+ return -ENOMEM;
+ do {
bus->nodes_modified = false;
r = object_find_and_run(bus, m, m->path, false, &found_object);
@@ -1498,9 +1507,14 @@ static int bus_find_parent_object_manager(sd_bus *bus, struct node **out, const
n = hashmap_get(bus->nodes, path);
if (!n) {
- char *prefix;
+ _cleanup_free_ char *prefix = NULL;
+ size_t pl;
- prefix = newa(char, strlen(path) + 1);
+ pl = strlen(path);
+ assert(pl <= BUS_PATH_SIZE_MAX);
+ prefix = new(char, pl + 1);
+ if (!prefix)
+ return -ENOMEM;
OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
n = hashmap_get(bus->nodes, prefix);
if (n)
@@ -2083,8 +2097,9 @@ _public_ int sd_bus_emit_properties_changed_strv(
const char *interface,
char **names) {
+ _cleanup_free_ char *prefix = NULL;
bool found_interface = false;
- char *prefix;
+ size_t pl;
int r;
assert_return(bus, -EINVAL);
@@ -2105,6 +2120,12 @@ _public_ int sd_bus_emit_properties_changed_strv(
BUS_DONT_DESTROY(bus);
+ pl = strlen(path);
+ assert(pl <= BUS_PATH_SIZE_MAX);
+ prefix = new(char, pl + 1);
+ if (!prefix)
+ return -ENOMEM;
+
do {
bus->nodes_modified = false;
@@ -2114,7 +2135,6 @@ _public_ int sd_bus_emit_properties_changed_strv(
if (bus->nodes_modified)
continue;
- prefix = newa(char, strlen(path) + 1);
OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
r = emit_properties_changed_on_interface(bus, prefix, path, interface, true, &found_interface, names);
if (r != 0)
@@ -2246,7 +2266,8 @@ static int object_added_append_all_prefix(
static int object_added_append_all(sd_bus *bus, sd_bus_message *m, const char *path) {
_cleanup_set_free_ Set *s = NULL;
- char *prefix;
+ _cleanup_free_ char *prefix = NULL;
+ size_t pl;
int r;
assert(bus);
@@ -2291,7 +2312,11 @@ static int object_added_append_all(sd_bus *bus, sd_bus_message *m, const char *p
if (bus->nodes_modified)
return 0;
- prefix = newa(char, strlen(path) + 1);
+ pl = strlen(path);
+ assert(pl <= BUS_PATH_SIZE_MAX);
+ prefix = new(char, pl + 1);
+ if (!prefix)
+ return -ENOMEM;
OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
r = object_added_append_all_prefix(bus, m, s, prefix, path, true);
if (r < 0)
@@ -2430,7 +2455,8 @@ static int object_removed_append_all_prefix(
static int object_removed_append_all(sd_bus *bus, sd_bus_message *m, const char *path) {
_cleanup_set_free_ Set *s = NULL;
- char *prefix;
+ _cleanup_free_ char *prefix = NULL;
+ size_t pl;
int r;
assert(bus);
@@ -2462,7 +2488,11 @@ static int object_removed_append_all(sd_bus *bus, sd_bus_message *m, const char
if (bus->nodes_modified)
return 0;
- prefix = newa(char, strlen(path) + 1);
+ pl = strlen(path);
+ assert(pl <= BUS_PATH_SIZE_MAX);
+ prefix = new(char, pl + 1);
+ if (!prefix)
+ return -ENOMEM;
OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
r = object_removed_append_all_prefix(bus, m, s, prefix, path, true);
if (r < 0)
@@ -2612,7 +2642,8 @@ static int interfaces_added_append_one(
const char *path,
const char *interface) {
- char *prefix;
+ _cleanup_free_ char *prefix = NULL;
+ size_t pl;
int r;
assert(bus);
@@ -2626,7 +2657,12 @@ static int interfaces_added_append_one(
if (bus->nodes_modified)
return 0;
- prefix = newa(char, strlen(path) + 1);
+ pl = strlen(path);
+ assert(pl <= BUS_PATH_SIZE_MAX);
+ prefix = new(char, pl + 1);
+ if (!prefix)
+ return -ENOMEM;
+
OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
r = interfaces_added_append_one_prefix(bus, m, prefix, path, interface, true);
if (r != 0)
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