1 files changed, 61 insertions, 0 deletions
diff --git a/fs/file.c b/fs/file.c
index 340bc9569f9d..4cb9ef4d8571 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -20,6 +20,7 @@
 #include <linux/spinlock.h>
 #include <linux/rcupdate.h>
 #include <linux/close_range.h>
+#include <net/sock.h>
 
 unsigned int sysctl_nr_open __read_mostly = 1024*1024;
 unsigned int sysctl_nr_open_min = BITS_PER_LONG;
@@ -625,6 +626,10 @@ void __fd_install(struct files_struct *files, unsigned int fd,
 	rcu_read_unlock_sched();
 }
 
+/*
+ * This consumes the "file" refcount, so callers should treat it
+ * as if they had called fput(file).
+ */
 void fd_install(unsigned int fd, struct file *file)
 {
 	__fd_install(current->files, fd, file);
@@ -1030,6 +1035,62 @@ out_unlock:
 	return err;
 }
 
+/**
+ * __receive_fd() - Install received file into file descriptor table
+ *
+ * @fd: fd to install into (if negative, a new fd will be allocated)
+ * @file: struct file that was received from another process
+ * @ufd: __user pointer to write new fd number to
+ * @o_flags: the O_* flags to apply to the new fd entry
+ *
+ * Installs a received file into the file descriptor table, with appropriate
+ * checks and count updates. Optionally writes the fd number to userspace, if
+ * @ufd is non-NULL.
+ *
+ * This helper handles its own reference counting of the incoming
+ * struct file.
+ *
+ * Returns newly install fd or -ve on error.
+ */
+int __receive_fd(int fd, struct file *file, int __user *ufd, unsigned int o_flags)
+{
+	int new_fd;
+	int error;
+
+	error = security_file_receive(file);
+	if (error)
+		return error;
+
+	if (fd < 0) {
+		new_fd = get_unused_fd_flags(o_flags);
+		if (new_fd < 0)
+			return new_fd;
+	} else {
+		new_fd = fd;
+	}
+
+	if (ufd) {
+		error = put_user(new_fd, ufd);
+		if (error) {
+			if (fd < 0)
+				put_unused_fd(new_fd);
+			return error;
+		}
+	}
+
+	if (fd < 0) {
+		fd_install(new_fd, get_file(file));
+	} else {
+		error = replace_fd(new_fd, file, o_flags);
+		if (error)
+			return error;
+	}
+
+	/* Bump the sock usage counts, if any. */
+	__receive_sock(file);
+	return new_fd;
+}
+
 static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
 {
 	int err = -EBADF;