Building the interpreter's argument vector is the bulk of
load_misc_binary() and the one part of it that is specific to the
classic dispatch. Move it into its own helper so what remains reads as
what it is: pick a handler, pick an interpreter, build the invocation,
open it.

No functional change.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/binfmt_misc.c | 84 ++++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 54 insertions(+), 30 deletions(-)

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 63c10066e3a6..f0ccc5d000f6 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -382,40 +382,23 @@ static struct file *entry_open_interpreter(const struct binfmt_misc_entry *e,
 	return no_free_ptr(interp_file);
 }
 
-/*
- * the loader itself
+/**
+ * build_interp_argv - splice the interpreter invocation into the argv
+ * @bprm: binary that is being executed
+ * @interpreter: the interpreter selected for this exec
+ * @flags: invocation flags in effect for this exec
+ *
+ * The interpreter becomes argv[0] and the binary its last argument, with an
+ * optional staged argument in between. The caller's argv[0] is dropped
+ * unless 'P' keeps it.
+ *
+ * Return: 0 on success, a negative error code on failure
  */
-static int load_misc_binary(struct linux_binprm *bprm)
+static int build_interp_argv(struct linux_binprm *bprm, const char *interpreter,
+			     unsigned long flags)
 {
-	struct binfmt_misc_entry *fmt __free(put_binfmt_handler) = NULL;
-	const char *interpreter;
-	struct file *interp_file;
-	struct binfmt_misc *misc;
-	unsigned long flags;
 	int retval;
 
-	misc = current_binfmt_misc();
-	if (!READ_ONCE(misc->enabled))
-		return -ENOEXEC;
-
-	fmt = get_binfmt_handler(misc, bprm);
-	if (!fmt)
-		return -ENOEXEC;
-
-	/* Need to be able to load the file after exec */
-	if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
-		return -ENOENT;
-
-	interpreter = entry_select_interpreter(fmt, bprm);
-	if (IS_ERR(interpreter))
-		return PTR_ERR(interpreter);
-
-	flags = entry_invocation_flags(fmt, bprm);
-	if (flags & MISC_FMT_CREDENTIALS)
-		bprm->execfd_creds = 1;
-	if (flags & MISC_FMT_OPEN_BINARY)
-		bprm->have_execfd = 1;
-
 	/* The entry's own choice - not one accumulated from an earlier level. */
 	if (flags & MISC_FMT_PRESERVE_ARGV0) {
 		bprm->interp_flags |= BINPRM_FLAGS_PRESERVE_ARGV0;
@@ -451,6 +434,47 @@ static int load_misc_binary(struct linux_binprm *bprm)
 		return retval;
 	bprm->argc++;
 
+	return 0;
+}
+
+/*
+ * the loader itself
+ */
+static int load_misc_binary(struct linux_binprm *bprm)
+{
+	struct binfmt_misc_entry *fmt __free(put_binfmt_handler) = NULL;
+	const char *interpreter;
+	struct file *interp_file;
+	struct binfmt_misc *misc;
+	unsigned long flags;
+	int retval;
+
+	misc = current_binfmt_misc();
+	if (!READ_ONCE(misc->enabled))
+		return -ENOEXEC;
+
+	fmt = get_binfmt_handler(misc, bprm);
+	if (!fmt)
+		return -ENOEXEC;
+
+	/* Need to be able to load the file after exec */
+	if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
+		return -ENOENT;
+
+	interpreter = entry_select_interpreter(fmt, bprm);
+	if (IS_ERR(interpreter))
+		return PTR_ERR(interpreter);
+
+	flags = entry_invocation_flags(fmt, bprm);
+	if (flags & MISC_FMT_CREDENTIALS)
+		bprm->execfd_creds = 1;
+	if (flags & MISC_FMT_OPEN_BINARY)
+		bprm->have_execfd = 1;
+
+	retval = build_interp_argv(bprm, interpreter, flags);
+	if (retval)
+		return retval;
+
 	/* Update interp in case binfmt_script needs it. */
 	retval = bprm_change_interp(interpreter, bprm);
 	if (retval < 0)

-- 
2.53.0