sd-device: use strjoina() more again in sd_device_new_from_subsystem_sysname()

This reverts a major part of: e17c95af8e450caacde692875b30675cea75211f

Using format strings for concatenating strings is pretty unefficient,
and using PATH_MAX buffers unpretty as well. Let's revert to using
strjoina() as before.

However, to fix the fuzz issue at hand, let's explicitly verify the two
input strings ensuring they are valid path names. This includes a length
check (to 2K each), thus making things prettier, faster and using less
memory again.

2 files changed, 73 insertions, 41 deletions

diff --git a/src/libsystemd/sd-device/sd-device.c b/src/libsystemd/sd-device/sd-device.c
index d0cba5b860..363e4f2dd0 100644
--- a/src/libsystemd/sd-device/sd-device.c
+++ b/src/libsystemd/sd-device/sd-device.c
@@ -244,71 +244,103 @@ _public_ int sd_device_new_from_devnum(sd_device **ret, char type, dev_t devnum)
         return sd_device_new_from_syspath(ret, syspath);
 }
 
-_public_ int sd_device_new_from_subsystem_sysname(sd_device **ret, const char *subsystem, const char *sysname) {
-        char syspath[PATH_MAX], *name;
+static int device_strjoin_new(
+                const char *a,
+                const char *b,
+                const char *c,
+                const char *d,
+                sd_device **ret) {
+
+        const char *p;
+        int r;
+
+        p = strjoina(a, b, c, d);
+        if (access(p, F_OK) < 0)
+                return IN_SET(errno, ENOENT, ENAMETOOLONG) ? 0 : -errno; /* If this sysfs is too long then it doesn't exist either */
+
+        r = sd_device_new_from_syspath(ret, p);
+        if (r < 0)
+                return r;
+
+        return 1;
+}
+
+_public_ int sd_device_new_from_subsystem_sysname(
+                sd_device **ret,
+                const char *subsystem,
+                const char *sysname) {
+
+        const char *s;
+        char *name;
+        int r;
 
         assert_return(ret, -EINVAL);
-        assert_return(subsystem, -EINVAL);
-        assert_return(sysname, -EINVAL);
-        assert_return(strlen(sysname) < PATH_MAX - strlen("/sys/bus/"), -ENAMETOOLONG);
+        assert_return(path_is_normalized(subsystem), -EINVAL);
+        assert_return(path_is_normalized(sysname), -EINVAL);
 
         if (streq(subsystem, "subsystem")) {
-                if (snprintf_ok(syspath, sizeof syspath, "/sys/subsystem/%s", sysname) &&
-                    access(syspath, F_OK) >= 0)
-                        return sd_device_new_from_syspath(ret, syspath);
-
-                if (snprintf_ok(syspath, sizeof syspath, "/sys/bus/%s", sysname) &&
-                    access(syspath, F_OK) >= 0)
-                        return sd_device_new_from_syspath(ret, syspath);
 
-                if (snprintf_ok(syspath, sizeof syspath, "/sys/class/%s", sysname) &&
-                    access(syspath, F_OK) >= 0)
-                        return sd_device_new_from_syspath(ret, syspath);
+                FOREACH_STRING(s, "/sys/subsystem/", "/sys/bus/", "/sys/class/") {
+                        r = device_strjoin_new(s, sysname, NULL, NULL, ret);
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                return 0;
+                }
 
         } else  if (streq(subsystem, "module")) {
-                if (snprintf_ok(syspath, sizeof syspath, "/sys/module/%s", sysname) &&
-                    access(syspath, F_OK) >= 0)
-                        return sd_device_new_from_syspath(ret, syspath);
+
+                r = device_strjoin_new("/sys/module/", sysname, NULL, NULL, ret);
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        return 0;
 
         } else if (streq(subsystem, "drivers")) {
-                const char *subsys, *sep;
+                const char *sep;
 
                 sep = strchr(sysname, ':');
                 if (sep && sep[1] != '\0') { /* Require ":" and something non-empty after that. */
-                        subsys = memdupa_suffix0(sysname, sep - sysname);
+                        const char *subsys;
 
-                        if (snprintf_ok(syspath, sizeof syspath, "/sys/subsystem/%s/drivers/%s", subsys, sep + 1) &&
-                            access(syspath, F_OK) >= 0)
-                                return sd_device_new_from_syspath(ret, syspath);
+                        subsys = memdupa_suffix0(sysname, sep - sysname);
+                        sep++;
 
-                        if (snprintf_ok(syspath, sizeof syspath, "/sys/bus/%s/drivers/%s", subsys, sep + 1) &&
-                            access(syspath, F_OK) >= 0)
-                                return sd_device_new_from_syspath(ret, syspath);
+                        FOREACH_STRING(s, "/sys/subsystem/", "/sys/bus/") {
+                                r = device_strjoin_new(s, subsys, "/drivers/", sep, ret);
+                                if (r < 0)
+                                        return r;
+                                if (r > 0)
+                                        return 0;
+                        }
                 }
         }
 
         /* translate sysname back to sysfs filename */
         name = strdupa(sysname);
-
         for (size_t i = 0; name[i]; i++)
                 if (name[i] == '/')
                         name[i] = '!';
 
-        if (snprintf_ok(syspath, sizeof syspath, "/sys/subsystem/%s/devices/%s", subsystem, name) &&
-            access(syspath, F_OK) >= 0)
-                return sd_device_new_from_syspath(ret, syspath);
-
-        if (snprintf_ok(syspath, sizeof syspath, "/sys/bus/%s/devices/%s", subsystem, name) &&
-            access(syspath, F_OK) >= 0)
-                return sd_device_new_from_syspath(ret, syspath);
+        FOREACH_STRING(s, "/sys/subsystem/", "/sys/bus/") {
+                r = device_strjoin_new(s, subsystem, "/devices/", name, ret);
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        return 0;
+        }
 
-        if (snprintf_ok(syspath, sizeof syspath, "/sys/class/%s/%s", subsystem, name) &&
-            access(syspath, F_OK) >= 0)
-                return sd_device_new_from_syspath(ret, syspath);
+        r = device_strjoin_new("/sys/class/", subsystem, "/", name, ret);
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return 0;
 
-        if (snprintf_ok(syspath, sizeof syspath, "/sys/firmware/%s/%s", subsystem, sysname) &&
-            access(syspath, F_OK) >= 0)
-                return sd_device_new_from_syspath(ret, syspath);
+        r = device_strjoin_new("/sys/firmware/", subsystem, "/", sysname, ret);
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return 0;
 
         return -ENODEV;
 }
diff --git a/src/test/test-udev-util.c b/src/test/test-udev-util.c
index f34c5c27d3..b87a90f766 100644
--- a/src/test/test-udev-util.c
+++ b/src/test/test-udev-util.c
@@ -252,7 +252,7 @@ static void test_udev_resolve_subsys_kernel(void) {
         test_udev_resolve_subsys_kernel_one("hoge", false, -EINVAL, NULL);
         test_udev_resolve_subsys_kernel_one("[hoge", false, -EINVAL, NULL);
         test_udev_resolve_subsys_kernel_one("[hoge/foo", false, -EINVAL, NULL);
-        test_udev_resolve_subsys_kernel_one("[hoge/]", false, -ENODEV, NULL);
+        test_udev_resolve_subsys_kernel_one("[hoge/]", false, -EINVAL, NULL);
 
         test_udev_resolve_subsys_kernel_one("[net/lo]", false, 0, "/sys/devices/virtual/net/lo");
         test_udev_resolve_subsys_kernel_one("[net/lo]/", false, 0, "/sys/devices/virtual/net/lo");