libc: always set argv and envp to valid addresses

packages/genodelabs/depot-targets.nix

@@ -151,6 +151,7 @@ in {
   posix = {
     buildInputs = [ self.libc ];
     portInputs = with ports; [ ports.libc ];
+    patches = [ ./patches/libc.patch ];
   };
   ps2_drv = { };
   qt5_base = { };

packages/genodelabs/patches/libc.patch

@@ -85,3 +85,78 @@ index 150640ddf3..e511897600 100644
  DUMMY(int   , -1, getpriority, (int, int))
  DUMMY(int   , -1, getrusage, (int, rusage *))
  DUMMY_SILENT(uid_t ,  0, getuid, (void))
+From 01bac4b0add9da8bbb4fcbe339605533ab7e7be5 Mon Sep 17 00:00:00 2001
+From: Emery Hemingway <ehmry@posteo.net>
+Date: Thu, 26 Nov 2020 12:47:30 +0100
+Subject: [PATCH] libc: always set argv and envp to valid arrays
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+The argument array passed to main(…) must be a null terminated array, even
+if argc is zero. Set at least one environment variable in any case.
+
+Fix #3955
+---
+ repos/libports/include/libc/args.h | 29 +++++++++++++++++++++++++----
+ 1 file changed, 25 insertions(+), 4 deletions(-)
+
+diff --git a/repos/libports/include/libc/args.h b/repos/libports/include/libc/args.h
+index 76645d82cb..fab299b8d3 100644
+--- a/repos/libports/include/libc/args.h
++++ b/repos/libports/include/libc/args.h
+@@ -25,6 +25,7 @@ static void populate_args_and_env(Libc::Env &env, int &argc, char **&argv, char
+ {
+ 	using Genode::Xml_node;
+ 	using Genode::Xml_attribute;
++	using Genode::max;
+ 
+ 	env.config([&] (Xml_node const &node) {
+ 
+@@ -40,12 +41,25 @@ static void populate_args_and_env(Libc::Env &env, int &argc, char **&argv, char
+ 				++envc;
+ 		});
+ 
+-		if (argc == 0 && envc == 0)
++		if (argc == 0 && envc == 0) {
++			/*
++			 * If argc is zero then argv is still a NULL-terminated array.
++			 *
++			 * Invent an enviromental variable in case the application
++			 * does not handle an empty environment. SHLVL=0 is
++			 * just an indication that this application lacks a parent
++			 * shell.
++			 */
++			static char const *args[] = { nullptr, "SHLVL=0", nullptr };
++			argc = 0;
++			argv = (char**)&args;
++			envp = &argv[1];
+ 			return; /* from lambda */
++		}
+ 
+-		/* arguments and environment are a contiguous array (but don't count on it) */
+-		argv = (char**)malloc((argc + envc + 1) * sizeof(char*));
+-		envp = &argv[argc];
++		/* arguments and environment are arranged System V style (but don't count on it) */
++		argv = (char**)malloc((argc + max(envc, 1) + 2) * sizeof(char*));
++		envp = &argv[argc+1];
+ 
+ 		/* read the arguments */
+ 		int arg_i = 0;
+@@ -123,6 +137,13 @@ static void populate_args_and_env(Libc::Env &env, int &argc, char **&argv, char
+ 			catch (Xml_node::Nonexistent_attribute) { }
+ 		});
+ 
++		/* argv and envp are both NULL terminated */
++
++		argv[arg_i] = NULL;
++
++		/* invent an env-var if none are present, see note above */
++		if (env_i == 0)
++			envp[env_i++] = (char*)"SHLVL=0";
+ 		envp[env_i] = NULL;
+ 	});
+ }
+-- 
+2.29.2
+