[PATCH] kernel/sysctl: return -EINVAL if write invalid val to ulong type sysctl

[Yisheng Xie]

I tried to echo an invalid value to an unsigned long type sysctl on
4.9.0-rc6:
   linux:~# cat /proc/sys/vm/user_reserve_kbytes
   131072
   linux:~# echo -1 > /proc/sys/vm/user_reserve_kbytes
   linux:~# cat /proc/sys/vm/user_reserve_kbytes
   131072

The echo operation got error and the value do not write to
user_reserve_kbytes, however, user do not know it until checking
the value again.

This patch return -EINVAL when write an invalid value to unsigned
long type sysctl to make user know  what happened without
checking its value once more, just as what proc_douintvec do.

Signed-off-by: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
---
This is a patchset after RFC, you can see the former discussion at
https://lkml.org/lkml/2016/11/26/48

Any comment is more than welcome.

Thanks,
Yisheng Xie.
---
 kernel/sysctl.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 706309f..40e9285 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2485,10 +2485,14 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int
 					     sizeof(proc_wspace_sep), NULL);
 			if (err)
 				break;
-			if (neg)
-				continue;
-			if ((min && val < *min) || (max && val > *max))
-				continue;
+			if (neg) {
+				err = -EINVAL;
+				break;
+			}
+			if ((min && val < *min) || (max && val > *max)) {
+				err = -EINVAL;
+				break;
+			}
 			*i = val;
 		} else {
 			val = convdiv * (*i) / convmul;
-- 
1.7.12.4