From 72f48cd3e37ff9ee77df491aa8eb0e23b8ca83e1 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Tue, 28 Apr 2020 17:01:56 +0200
Subject: [PATCH] hostnamed: don't cache uname() data

Let's not cache the uname(), it's very cheap to get it, and just means
we might get out of sync with what is current. After all, the data might
change IRL, due to setarch and stuff.
---
 src/hostname/hostnamed.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/src/hostname/hostnamed.c b/src/hostname/hostnamed.c
index 701041c12ad..e20e9f6dadc 100644
--- a/src/hostname/hostnamed.c
+++ b/src/hostname/hostnamed.c
@@ -43,9 +43,6 @@ enum {
         PROP_CHASSIS,
         PROP_DEPLOYMENT,
         PROP_LOCATION,
-        PROP_KERNEL_NAME,
-        PROP_KERNEL_RELEASE,
-        PROP_KERNEL_VERSION,
         PROP_OS_PRETTY_NAME,
         PROP_OS_CPE_NAME,
         PROP_HOME_URL,
@@ -77,20 +74,11 @@ static void context_clear(Context *c) {
 
 static int context_read_data(Context *c) {
         int r;
-        struct utsname u;
 
         assert(c);
 
         context_reset(c);
 
-        assert_se(uname(&u) >= 0);
-        c->data[PROP_KERNEL_NAME] = strdup(u.sysname);
-        c->data[PROP_KERNEL_RELEASE] = strdup(u.release);
-        c->data[PROP_KERNEL_VERSION] = strdup(u.version);
-        if (!c->data[PROP_KERNEL_NAME] || !c->data[PROP_KERNEL_RELEASE] ||
-            !c->data[PROP_KERNEL_VERSION])
-                return -ENOMEM;
-
         c->data[PROP_HOSTNAME] = gethostname_malloc();
         if (!c->data[PROP_HOSTNAME])
                 return -ENOMEM;
@@ -411,6 +399,22 @@ static int property_get_chassis(
         return sd_bus_message_append(reply, "s", name);
 }
 
+static int property_get_uname_field(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        struct utsname u;
+
+        assert_se(uname(&u) >= 0);
+
+        return sd_bus_message_append(reply, "s", (char*) &u + PTR_TO_SIZE(userdata));
+}
+
 static int method_set_hostname(sd_bus_message *m, void *userdata, sd_bus_error *error) {
         Context *c = userdata;
         const char *name;
@@ -673,9 +677,9 @@ static const sd_bus_vtable hostname_vtable[] = {
         SD_BUS_PROPERTY("Chassis", "s", property_get_chassis, 0, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("Deployment", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_DEPLOYMENT, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("Location", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_LOCATION, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
-        SD_BUS_PROPERTY("KernelName", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_KERNEL_NAME, SD_BUS_VTABLE_PROPERTY_CONST),
-        SD_BUS_PROPERTY("KernelRelease", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_KERNEL_RELEASE, SD_BUS_VTABLE_PROPERTY_CONST),
-        SD_BUS_PROPERTY("KernelVersion", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_KERNEL_VERSION, SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("KernelName", "s", property_get_uname_field, offsetof(struct utsname, sysname), SD_BUS_VTABLE_ABSOLUTE_OFFSET|SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("KernelRelease", "s", property_get_uname_field, offsetof(struct utsname, release), SD_BUS_VTABLE_ABSOLUTE_OFFSET|SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("KernelVersion", "s", property_get_uname_field, offsetof(struct utsname, version), SD_BUS_VTABLE_ABSOLUTE_OFFSET|SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("OperatingSystemPrettyName", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_OS_PRETTY_NAME, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("OperatingSystemCPEName", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_OS_CPE_NAME, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("HomeURL", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_HOME_URL, SD_BUS_VTABLE_PROPERTY_CONST),
-- 
2.47.3