splice: Apply generic position and size checks to each write

We need to check the position and size of file writes against various
limits, using generic_write_check().  This was not being done for
the splice write path.  It was fixed upstream by commit 8d020765
("->splice_write() via ->write_iter()") but we can't apply that.

CVE-2014-7822
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/ocfs2/file.c

@@ -2468,9 +2468,7 @@ static ssize_t ocfs2_file_splice_write(struct pipe_inode_info *pipe,
 	struct address_space *mapping = out->f_mapping;
 	struct inode *inode = mapping->host;
 	struct splice_desc sd = {
-		.total_len = len,
 		.flags = flags,
-		.pos = *ppos,
 		.u.file = out,
 	};
 
@@ -2480,6 +2478,12 @@ static ssize_t ocfs2_file_splice_write(struct pipe_inode_info *pipe,
 			out->f_path.dentry->d_name.len,
 			out->f_path.dentry->d_name.name, len);
 
+	ret = generic_write_checks(out, ppos, &len, 0);
+	if (ret)
+		return ret;
+	sd.total_len = len;
+	sd.pos = *ppos;
+
 	if (pipe->inode)
 		mutex_lock_nested(&pipe->inode->i_mutex, I_MUTEX_PARENT);
 

fs/splice.c

@@ -1013,13 +1013,17 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 	struct address_space *mapping = out->f_mapping;
 	struct inode *inode = mapping->host;
 	struct splice_desc sd = {
-		.total_len = len,
 		.flags = flags,
-		.pos = *ppos,
 		.u.file = out,
 	};
 	ssize_t ret;
 
+	ret = generic_write_checks(out, ppos, &len, S_ISBLK(inode->i_mode));
+	if (ret)
+		return ret;
+	sd.total_len = len;
+	sd.pos = *ppos;
+
 	pipe_lock(pipe);
 
 	splice_from_pipe_begin(&sd);