subprocess-win: Always quote argv[0]

If the program name isn't quoted and the .exe it refers to isn't found,
CreateProcess will add the program arguments to the program name and
continue searching, so for "program arg1 arg2", CreateProcess would try
"program.exe", "program arg1.exe", then "program arg1 arg2.exe". This
behaviour is weird and not really desirable, so prevent it by always
quoting the program name.

When quoting argv[0], escape sequences shouldn't be used. msvcrt, .NET
and CommandLineToArgvW all treat argv[0] literally and end it on the
trailing quote, without processing escape sequences.

1 files changed, 5 insertions, 3 deletions

diff --git a/osdep/subprocess-win.c b/osdep/subprocess-win.c
index fc5db081f8..211f407db1 100644
--- a/osdep/subprocess-win.c
+++ b/osdep/subprocess-win.c
@@ -83,12 +83,14 @@ static void write_arg(bstr *cmdline, char *arg)
 // Convert an array of arguments to a properly escaped command-line string
 static wchar_t *write_cmdline(void *ctx, char **argv)
 {
+    // argv[0] should always be quoted. Otherwise, arguments may be interpreted
+    // as part of the program name. Also, it can't contain escape sequences.
     bstr cmdline = {0};
+    bstr_xappend_asprintf(NULL, &cmdline, "\"%s\"", argv[0]);
 
-    for (int i = 0; argv[i]; i++) {
+    for (int i = 1; argv[i]; i++) {
+        bstr_xappend(NULL, &cmdline, bstr0(" "));
         write_arg(&cmdline, argv[i]);
-        if (argv[i + 1])
-            bstr_xappend(NULL, &cmdline, bstr0(" "));
     }
 
     wchar_t *wcmdline = mp_from_utf8(ctx, cmdline.start);