su: Support supplementary groups

apps/su.cpp

@@ -1,4 +1,6 @@
+#include <errno.h>
 #include <fcntl.h>
+#include <grp.h>
 #include <os/ArgumentParser.h>
 #include <pwd.h>
 #include <signal.h>
@@ -89,6 +91,30 @@ char* getpass()
     return buf;
 }
 
+Result<void> set_supplementary_groups(const char* name)
+{
+    Vector<gid_t> extra_groups;
+
+    setgrent();
+    group* grp;
+    while ((grp = getgrent()))
+    {
+        for (char** user = grp->gr_mem; *user; user++)
+        {
+            if (!strcmp(*user, name))
+            {
+                TRY(extra_groups.try_append(grp->gr_gid));
+                break;
+            }
+        }
+    }
+    endgrent();
+
+    if (setgroups(static_cast<int>(extra_groups.size()), extra_groups.data()) < 0) return err(errno);
+
+    return {};
+}
+
 Result<int> luna_main(int argc, char** argv)
 {
     StringView name;
@@ -134,6 +160,8 @@ Result<int> luna_main(int argc, char** argv)
         memset(pass, 0, strlen(pass));
     }
 
+    TRY(set_supplementary_groups(name.chars()));
+
     setgid(entry->pw_gid);
     setuid(entry->pw_uid);