pid1: restore the original environment passed by the kernel when switching to a new system manager

PID1 may modified the environment passed by the kernel when it starts
running. Commit 9d48671c62de133a2b9fe7c31e70c0ff8e68f2db unset $HOME for
example.

In case PID1 is going to switch to a new root and execute a new system manager
which is not systemd, we should restore the original environment as the new
manager might expect some variables to be set by default (more specifically
$HOME).

2 files changed, 11 insertions, 0 deletions

diff --git a/src/basic/util.c b/src/basic/util.c
index 93d610bc98..4989b8aa77 100644
--- a/src/basic/util.c
+++ b/src/basic/util.c
@@ -39,6 +39,7 @@
 #include "set.h"
 #include "signal-util.h"
 #include "stat-util.h"
+#include "static-destruct.h"
 #include "string-util.h"
 #include "strv.h"
 #include "time-util.h"
@@ -49,8 +50,11 @@
 
 int saved_argc = 0;
 char **saved_argv = NULL;
+char **saved_env = NULL;
 static int saved_in_initrd = -1;
 
+STATIC_DESTRUCTOR_REGISTER(saved_env, strv_freep);
+
 bool kexec_loaded(void) {
        _cleanup_free_ char *s = NULL;
 
@@ -298,3 +302,7 @@ void disable_coredumps(void) {
         if (r < 0)
                 log_debug_errno(r, "Failed to turn off coredumps, ignoring: %m");
 }
+
+void save_env(void) {
+        saved_env = strv_copy(environ);
+}
diff --git a/src/basic/util.h b/src/basic/util.h
index 6fc7480fcb..15444b2e5c 100644
--- a/src/basic/util.h
+++ b/src/basic/util.h
@@ -13,6 +13,9 @@ static inline void save_argc_argv(int argc, char **argv) {
         saved_argv = argv;
 }
 
+extern char **saved_env;
+void save_env(void);
+
 bool kexec_loaded(void);
 
 int prot_from_flags(int flags) _const_;