proc_dointvec: write a single value

The commit 00b7c339
"sysctl: refactor integer handling proc code"
modified the behaviour of writing to /proc.
Before the commit, write("1\n") to /proc/sys/kernel/printk succeeded. But
now it returns EINVAL.

This commit supports writing a single value to a multi-valued entry.
Signed-off-by: NJ. R. Okajima <hooanon05@yahoo.co.jp>
Reviewed-and-tested-by: NWANG Cong <amwang@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

kernel/sysctl.c

@@ -2253,6 +2253,8 @@ static int __do_proc_dointvec(void *tbl_data, struct ctl_table *table,
 		if (write) {
 			left -= proc_skip_spaces(&kbuf);
 
+			if (!left)
+				break;
 			err = proc_get_long(&kbuf, &left, &lval, &neg,
 					     proc_wspace_sep,
 					     sizeof(proc_wspace_sep), NULL);
@@ -2279,7 +2281,7 @@ static int __do_proc_dointvec(void *tbl_data, struct ctl_table *table,
 
 	if (!write && !first && left && !err)
 		err = proc_put_char(&buffer, &left, '\n');
-	if (write && !err)
+	if (write && !err && left)
 		left -= proc_skip_spaces(&kbuf);
 free:
 	if (write) {