Description: sd-bus: enforce a size limit for dbus paths, and don't allocate
 them on the stacka
Forwarded: no

Patch from: systemd_237-3ubuntu10.13

For information see:
https://usn.ubuntu.com/3891-1/
https://git.launchpad.net/ubuntu/+source/systemd/commit/?h=applied/ubuntu/bionic-updates&id=d7584b894afcaa8a4a1abb69db2a9c81a6276e80

CVE: CVE-2019-6454
Upstream-Status: Backport

Signed-off-by: George McCollister <george.mccollister@gmail.com>

--- a/src/libsystemd/sd-bus/bus-internal.c
+++ b/src/libsystemd/sd-bus/bus-internal.c
@@ -61,7 +61,7 @@
         if (slash)
                 return false;
 
-        return true;
+        return (q - p) <= BUS_PATH_SIZE_MAX;
 }
 
 char* object_path_startswith(const char *a, const char *b) {
--- a/src/libsystemd/sd-bus/bus-internal.h
+++ b/src/libsystemd/sd-bus/bus-internal.h
@@ -339,6 +339,10 @@
 
 #define BUS_MESSAGE_SIZE_MAX (64*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
 
--- a/src/libsystemd/sd-bus/bus-objects.c
+++ b/src/libsystemd/sd-bus/bus-objects.c
@@ -1150,7 +1150,8 @@
                 const char *path,
                 sd_bus_error *error) {
 
-        char *prefix;
+        _cleanup_free_ char *prefix = NULL;
+        size_t pl;
         int r;
 
         assert(bus);
@@ -1166,7 +1167,12 @@
                 return 0;
 
         /* Second, add fallback vtables registered for any of the prefixes */
-        prefix = alloca(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)
@@ -1362,6 +1368,7 @@
 }
 
 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;
@@ -1386,9 +1393,12 @@
         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);
@@ -1516,9 +1526,15 @@
 
         n = hashmap_get(bus->nodes, path);
         if (!n) {
-                char *prefix;
+                _cleanup_free_ char *prefix = NULL;
+                size_t pl;
+
+                pl = strlen(path);
+                assert(pl <= BUS_PATH_SIZE_MAX);
+                prefix = new(char, pl + 1);
+                if (!prefix)
+                        return -ENOMEM;
 
-                prefix = alloca(strlen(path) + 1);
                 OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
                         n = hashmap_get(bus->nodes, prefix);
                         if (n)
@@ -2108,8 +2124,9 @@
                 char **names) {
 
         BUS_DONT_DESTROY(bus);
+        _cleanup_free_ char *prefix = NULL;
         bool found_interface = false;
-        char *prefix;
+        size_t pl;
         int r;
 
         assert_return(bus, -EINVAL);
@@ -2128,6 +2145,12 @@
         if (names && names[0] == NULL)
                 return 0;
 
+        pl = strlen(path);
+        assert(pl <= BUS_PATH_SIZE_MAX);
+        prefix = new(char, pl + 1);
+        if (!prefix)
+                return -ENOMEM;
+
         do {
                 bus->nodes_modified = false;
 
@@ -2137,7 +2160,6 @@
                 if (bus->nodes_modified)
                         continue;
 
-                prefix = alloca(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)
@@ -2269,7 +2291,8 @@
 
 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);
@@ -2314,7 +2337,12 @@
         if (bus->nodes_modified)
                 return 0;
 
-        prefix = alloca(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)
@@ -2453,7 +2481,8 @@
 
 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);
@@ -2485,7 +2514,12 @@
         if (bus->nodes_modified)
                 return 0;
 
-        prefix = alloca(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)
@@ -2635,7 +2669,8 @@
                 const char *path,
                 const char *interface) {
 
-        char *prefix;
+        _cleanup_free_ char *prefix = NULL;
+        size_t pl;
         int r;
 
         assert(bus);
@@ -2649,7 +2684,12 @@
         if (bus->nodes_modified)
                 return 0;
 
-        prefix = alloca(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)