Kernel: Fix String leaks in exec().

When the kernel performs a successful exec(), whatever was on the kernel
stack for that process before goes away. For this reason, we need to make
sure we don't have any stack objects holding onto kmalloc memory.

Kernel/Process.cpp

@@ -282,7 +282,7 @@ pid_t Process::sys$fork(RegisterDump& regs)
     return child->pid();
 }
 
-int Process::do_exec(const String& path, Vector<String>&& arguments, Vector<String>&& environment)
+int Process::do_exec(String path, Vector<String> arguments, Vector<String> environment)
 {
     ASSERT(is_ring3());
 
@@ -419,11 +419,11 @@ int Process::do_exec(const String& path, Vector<String>&& arguments, Vector<Stri
     return 0;
 }
 
-int Process::exec(const String& path, Vector<String>&& arguments, Vector<String>&& environment)
+int Process::exec(String path, Vector<String> arguments, Vector<String> environment)
 {
     // The bulk of exec() is done by do_exec(), which ensures that all locals
     // are cleaned up by the time we yield-teleport below.
-    int rc = do_exec(path, move(arguments), move(environment));
+    int rc = do_exec(move(path), move(arguments), move(environment));
     if (rc < 0)
         return rc;
 
@@ -436,6 +436,8 @@ int Process::exec(const String& path, Vector<String>&& arguments, Vector<String>
 
 int Process::sys$execve(const char* filename, const char** argv, const char** envp)
 {
+    // NOTE: Be extremely careful with allocating any kernel memory in exec().
+    //       On success, the kernel stack will be lost.
     if (!validate_read_str(filename))
         return -EFAULT;
     if (argv) {
@@ -456,24 +458,25 @@ int Process::sys$execve(const char* filename, const char** argv, const char** en
     }
 
     String path(filename);
-    auto parts = path.split('/');
-
     Vector<String> arguments;
-    if (argv) {
-        for (size_t i = 0; argv[i]; ++i) {
-            arguments.append(argv[i]);
+    Vector<String> environment;
+    {
+        auto parts = path.split('/');
+        if (argv) {
+            for (size_t i = 0; argv[i]; ++i) {
+                arguments.append(argv[i]);
+            }
+        } else {
+            arguments.append(parts.last());
         }
-    } else {
-        arguments.append(parts.last());
-    }
 
-    Vector<String> environment;
-    if (envp) {
-        for (size_t i = 0; envp[i]; ++i)
-            environment.append(envp[i]);
+        if (envp) {
+            for (size_t i = 0; envp[i]; ++i)
+                environment.append(envp[i]);
+        }
     }
 
-    int rc = exec(path, move(arguments), move(environment));
+    int rc = exec(move(path), move(arguments), move(environment));
     ASSERT(rc < 0); // We should never continue after a successful exec!
     return rc;
 }

Kernel/Process.h

@@ -279,7 +279,7 @@ public:
     size_t amount_shared() const;
 
     Process* fork(RegisterDump&);
-    int exec(const String& path, Vector<String>&& arguments, Vector<String>&& environment);
+    int exec(String path, Vector<String> arguments, Vector<String> environment);
 
     bool is_root() const { return m_euid == 0; }
 
@@ -302,7 +302,7 @@ private:
 
     Process(String&& name, uid_t, gid_t, pid_t ppid, RingLevel, RetainPtr<Inode>&& cwd = nullptr, RetainPtr<Inode>&& executable = nullptr, TTY* = nullptr, Process* fork_parent = nullptr);
 
-    int do_exec(const String& path, Vector<String>&& arguments, Vector<String>&& environment);
+    int do_exec(String path, Vector<String> arguments, Vector<String> environment);
     void push_value_on_stack(dword);
 
     int alloc_fd();