[RFC PATCH 06/24] exec: expose execveat internals to process builders

[Li Chen <me@linux.beauty>]

Move struct user_arg_ptr and its native and compat constructors to an
fs-private header. Expose do_execveat_common() within fs so a process
builder can enter the normal exec path without synthesizing a userspace
execveat() syscall.

Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Li Chen <me@linux.beauty>
---
 MAINTAINERS        |  1 +
 fs/exec.c          | 28 ++++------------------------
 fs/exec_internal.h | 40 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 24 deletions(-)
 create mode 100644 fs/exec_internal.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 8d7f94f09f414..85b1306cb2ff3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9757,6 +9757,7 @@ F:	Documentation/userspace-api/ELF.rst
 F:	fs/*binfmt_*.c
 F:	fs/Kconfig.binfmt
 F:	fs/exec.c
+F:	fs/exec_internal.h
 F:	fs/tests/binfmt_*_kunit.c
 F:	fs/tests/exec_kunit.c
 F:	include/linux/binfmts.h
diff --git a/fs/exec.c b/fs/exec.c
index d5993cedc829a..1a256ba26425e 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -76,6 +76,7 @@
 
 #include <trace/events/task.h>
 #include "internal.h"
+#include "exec_internal.h"
 
 #include <trace/events/sched.h>
 
@@ -291,17 +292,6 @@ static int bprm_mm_init(struct linux_binprm *bprm)
 	return err;
 }
 
-struct user_arg_ptr {
-#ifdef CONFIG_COMPAT
-	bool is_compat;
-#endif
-	union {
-		const char __user *const __user *native;
-#ifdef CONFIG_COMPAT
-		const compat_uptr_t __user *compat;
-#endif
-	} ptr;
-};
 
 static const char __user *get_user_arg_ptr(struct user_arg_ptr argv, int nr)
 {
@@ -1805,10 +1795,9 @@ static int bprm_execve(struct linux_binprm *bprm)
 	return retval;
 }
 
-static int do_execveat_common(int fd, struct filename *filename,
-			      struct user_arg_ptr argv,
-			      struct user_arg_ptr envp,
-			      int flags)
+int do_execveat_common(int fd, struct filename *filename,
+		       struct user_arg_ptr argv,
+		       struct user_arg_ptr envp, int flags)
 {
 	int retval;
 
@@ -1935,10 +1924,6 @@ void set_binfmt(struct linux_binfmt *new)
 }
 EXPORT_SYMBOL(set_binfmt);
 
-static inline struct user_arg_ptr native_arg(const char __user *const __user *p)
-{
-	return (struct user_arg_ptr){.ptr.native = p};
-}
 
 SYSCALL_DEFINE3(execve,
 		const char __user *, filename,
@@ -1963,11 +1948,6 @@ SYSCALL_DEFINE5(execveat,
 
 #ifdef CONFIG_COMPAT
 
-static inline struct user_arg_ptr compat_arg(const compat_uptr_t __user *p)
-{
-	return (struct user_arg_ptr){.is_compat = true, .ptr.compat = p};
-}
-
 COMPAT_SYSCALL_DEFINE3(execve, const char __user *, filename,
 	const compat_uptr_t __user *, argv,
 	const compat_uptr_t __user *, envp)
diff --git a/fs/exec_internal.h b/fs/exec_internal.h
new file mode 100644
index 0000000000000..bf6a873e98426
--- /dev/null
+++ b/fs/exec_internal.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _FS_EXEC_INTERNAL_H
+#define _FS_EXEC_INTERNAL_H
+
+#include <linux/compat.h>
+#include <linux/compiler_types.h>
+#include <linux/types.h>
+
+struct filename;
+
+struct user_arg_ptr {
+#ifdef CONFIG_COMPAT
+	bool is_compat;
+#endif
+	union {
+		const char __user *const __user *native;
+#ifdef CONFIG_COMPAT
+		const compat_uptr_t __user *compat;
+#endif
+	} ptr;
+};
+
+static inline struct user_arg_ptr
+native_arg(const char __user *const __user *p)
+{
+	return (struct user_arg_ptr){.ptr.native = p};
+}
+
+#ifdef CONFIG_COMPAT
+static inline struct user_arg_ptr compat_arg(const compat_uptr_t __user *p)
+{
+	return (struct user_arg_ptr){.is_compat = true, .ptr.compat = p};
+}
+#endif
+
+int do_execveat_common(int fd, struct filename *filename,
+		       struct user_arg_ptr argv,
+		       struct user_arg_ptr envp, int flags);
+
+#endif /* _FS_EXEC_INTERNAL_H */
-- 
2.52.0