pass creds to get_empty_filp(), make sure dentry_open() passes the right creds

... and rename get_empty_filp() to alloc_empty_file().

dentry_open() gets creds as argument, but the only thing that sees those is
security_file_open() - file->f_cred still ends up with current_cred().  For
almost all callers it's the same thing, but there are several broken cases.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/file_table.c b/fs/file_table.c
index 086c3f5..76cfa4c 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -101,9 +101,8 @@
  * done, you will imbalance int the mount's writer count
  * and a warning at __fput() time.
  */
-struct file *get_empty_filp(void)
+struct file *alloc_empty_file(const struct cred *cred)
 {
-	const struct cred *cred = current_cred();
 	static long old_max;
 	struct file *f;
 	int error;
@@ -161,7 +160,7 @@
 {
 	struct file *file;
 
-	file = get_empty_filp();
+	file = alloc_empty_file(current_cred());
 	if (IS_ERR(file))
 		return file;
 
diff --git a/fs/internal.h b/fs/internal.h
index 5645b4e..66473bf 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -93,7 +93,7 @@
 /*
  * file_table.c
  */
-extern struct file *get_empty_filp(void);
+extern struct file *alloc_empty_file(const struct cred *);
 
 /*
  * super.c
diff --git a/fs/namei.c b/fs/namei.c
index 734cef5..af2ec18 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3513,7 +3513,7 @@
 	int opened = 0;
 	int error;
 
-	file = get_empty_filp();
+	file = alloc_empty_file(current_cred());
 	if (IS_ERR(file))
 		return file;
 
diff --git a/fs/open.c b/fs/open.c
index 530da96..0061f9e 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -921,7 +921,7 @@
 	/* We must always pass in a valid mount pointer. */
 	BUG_ON(!path->mnt);
 
-	f = get_empty_filp();
+	f = alloc_empty_file(cred);
 	if (!IS_ERR(f)) {
 		f->f_flags = flags;
 		error = vfs_open(path, f, cred);