exec is the only caller left since commit 433967cab51e ("coredump: stop
unsharing the file descriptor table"). All it does is call unshare_fd()
with CLONE_FILES and install the copy. Kill the pointless helper and
open-code it.

No functional changes.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/exec.c               |  5 ++++-
 include/linux/fdtable.h |  1 -
 kernel/fork.c           | 24 ------------------------
 3 files changed, 4 insertions(+), 26 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index d3081c8f7c10..977778f44cfc 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1124,6 +1124,7 @@ static struct file *bprm_identity_file(const struct linux_binprm *bprm)
 int begin_new_exec(struct linux_binprm * bprm)
 {
 	struct task_struct *me = current;
+	struct files_struct *files = NULL;
 	int retval;
 
 	/* A pending PT_INTERP substitution this format cannot consume. */
@@ -1160,9 +1161,11 @@ int begin_new_exec(struct linux_binprm * bprm)
 	io_uring_task_cancel();
 
 	/* Ensure the files table is not shared. */
-	retval = unshare_files();
+	retval = unshare_fd(CLONE_FILES, &files);
 	if (retval)
 		goto out;
+	if (files)
+		switch_files_struct(me, files);
 
 	/*
 	 * We have to apply CLOEXEC before we change whether the process is
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 4ee1598848bb..666808a1caf5 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -101,7 +101,6 @@ struct task_struct;
 
 void put_files_struct(struct files_struct *fs);
 void switch_files_struct(struct task_struct *tsk, struct files_struct *files);
-int unshare_files(void);
 int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp);
 struct fd_range {
 	unsigned int from, to;
diff --git a/kernel/fork.c b/kernel/fork.c
index fddba55bbc14..300cb46bc51e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -3336,30 +3336,6 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
 	return ksys_unshare(unshare_flags);
 }
 
-/*
- *	Helper to unshare the files of the current task.
- *	We don't want to expose copy_files internals to
- *	the exec layer of the kernel.
- */
-
-int unshare_files(void)
-{
-	struct task_struct *task = current;
-	struct files_struct *old, *copy = NULL;
-	int error;
-
-	error = unshare_fd(CLONE_FILES, &copy);
-	if (error || !copy)
-		return error;
-
-	old = task->files;
-	task_lock(task);
-	task->files = copy;
-	task_unlock(task);
-	put_files_struct(old);
-	return 0;
-}
-
 static int sysctl_max_threads(const struct ctl_table *table, int write,
 		       void *buffer, size_t *lenp, loff_t *ppos)
 {

-- 
2.53.0