2016-11-26 09:15:24

by Yisheng Xie

Subject: [RFC] kernel/sysctl.c: return -EINVAL when write invalid val to ulong type sysctl

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 check the value again.

Is it more suitable to return -EINVAL when echo an invalid value to an unsigned long
type sysctl, in order to let user know what happened without checking its value once more?
Just as what int type sysctl do:
linux:~#cat /proc/sys/kernel/sysctl_writes_strict
1
linux:~# echo 3 > /proc/sys/kernel/sysctl_writes_strict
bash: echo: write error: Invalid argument

----------------------
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;

2016-11-26 23:15:55

by Subash Abhinov Kasiviswanathan

Subject: Re: [RFC] kernel/sysctl.c: return -EINVAL when write invalid val to ulong type sysctl

On 2016-11-26 02:13, Yisheng Xie wrote:
> 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 check the value again.
>
> Is it more suitable to return -EINVAL when echo an invalid value to an
> unsigned long
> type sysctl, in order to let user know what happened without checking
> its value once more?
> Just as what int type sysctl do:
> linux:~#cat /proc/sys/kernel/sysctl_writes_strict
> 1
> linux:~# echo 3 > /proc/sys/kernel/sysctl_writes_strict
> bash: echo: write error: Invalid argument
>
> ----------------------
> 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;

Agree, this should be similar to proc_douintvec

root@vm:~# echo 8192 > /proc/sys/net/core/xfrm_aevent_rseqth
root@vm:~# cat /proc/sys/net/core/xfrm_aevent_rseqth
8192
root@vm:~# echo -1 > /proc/sys/net/core/xfrm_aevent_rseqth
-bash: echo: write error: Invalid argument
root@vm:~# cat /proc/sys/net/core/xfrm_aevent_rseqth
8192

--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
Linux Foundation Collaborative Project

2016-11-29 10:26:28

by Yisheng Xie

Subject: Re: [RFC] kernel/sysctl.c: return -EINVAL when write invalid val to ulong type sysctl

On 2016/11/27 7:15, [email protected] wrote:
> On 2016-11-26 02:13, Yisheng Xie wrote:
>> ----------------------
>> 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;
>
> Agree, this should be similar to proc_douintvec
>
> root@vm:~# echo 8192 > /proc/sys/net/core/xfrm_aevent_rseqth
> root@vm:~# cat /proc/sys/net/core/xfrm_aevent_rseqth
> 8192
> root@vm:~# echo -1 > /proc/sys/net/core/xfrm_aevent_rseqth
> -bash: echo: write error: Invalid argument
> root@vm:~# cat /proc/sys/net/core/xfrm_aevent_rseqth
> 8192
>
Hi,
Thank you for your reply,
then I will write a formal patch to see whether it is acceptable.

Thanks,
Yisheng Xie
> --
> Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
>
> .
>