fs: provide locked helper variant of close_fd_get_file()

mainline inclusion
from mainline-v5.12-rc1
commit 53dec2ea
category: bugfix
bugzilla: 188963, https://gitee.com/src-openeuler/kernel/issues/I7GUAN
CVE: NA

--------------------------------

Assumes current->files->file_lock is already held on invocation. Helps
the caller check the file before removing the fd, if it needs to.
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Conflicts:
	fs/file.c
	fs/internal.h
Signed-off-by: NLi Nan <linan122@huawei.com>
Reviewed-by: NYang Erkun <yangerkun@huawei.com>
Reviewed-by: NWang Weiyang <wangweiyang2@huawei.com>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

fs/file.c

@@ -20,6 +20,8 @@
 #include <linux/rcupdate.h>
 #include <linux/filescontrol.h>
 
+#include "internal.h"
+
 unsigned int sysctl_nr_open __read_mostly = 1024*1024;
 unsigned int sysctl_nr_open_min = BITS_PER_LONG;
 /* our min() is unusable in constant expressions ;-/ */
@@ -696,36 +698,48 @@ int __close_fd(struct files_struct *files, unsigned fd)
 EXPORT_SYMBOL(__close_fd); /* for ksys_close() */
 
 /*
- * variant of close_fd that gets a ref on the file for later fput.
- * The caller must ensure that filp_close() called on the file, and then
- * an fput().
+ * See close_fd_get_file() below, this variant assumes current->files->file_lock
+ * is held.
  */
-int close_fd_get_file(unsigned int fd, struct file **res)
+int __close_fd_get_file(unsigned int fd, struct file **res)
 {
 	struct files_struct *files = current->files;
 	struct file *file;
 	struct fdtable *fdt;
 
-	spin_lock(&files->file_lock);
 	fdt = files_fdtable(files);
 	if (fd >= fdt->max_fds)
-		goto out_unlock;
+		goto out_err;
 	file = fdt->fd[fd];
 	if (!file)
-		goto out_unlock;
+		goto out_err;
 	rcu_assign_pointer(fdt->fd[fd], NULL);
 	__put_unused_fd(files, fd);
-	spin_unlock(&files->file_lock);
 	get_file(file);
 	*res = file;
 	return 0;
-
-out_unlock:
-	spin_unlock(&files->file_lock);
+out_err:
 	*res = NULL;
 	return -ENOENT;
 }
 
+/*
+ * variant of close_fd that gets a ref on the file for later fput.
+ * The caller must ensure that filp_close() called on the file, and then
+ * an fput().
+ */
+int close_fd_get_file(unsigned int fd, struct file **res)
+{
+	struct files_struct *files = current->files;
+	int ret;
+
+	spin_lock(&files->file_lock);
+	ret = __close_fd_get_file(fd, res);
+	spin_unlock(&files->file_lock);
+
+	return ret;
+}
+
 void do_close_on_exec(struct files_struct *files)
 {
 	unsigned i;

fs/internal.h

@@ -120,6 +120,7 @@ extern struct file *do_filp_open(int dfd, struct filename *pathname,
 extern struct file *do_file_open_root(struct dentry *, struct vfsmount *,
 		const char *, const struct open_flags *);
 extern int build_open_flags(int flags, umode_t mode, struct open_flags *op);
+extern int __close_fd_get_file(unsigned int fd, struct file **res);
 
 long do_sys_ftruncate(unsigned int fd, loff_t length, int small);
 long do_faccessat(int dfd, const char __user *filename, int mode);