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SubjectRe: [PATCH v2 3/5] sysctl: Warn when a clamped sysctl parameter is set out of range
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On 02/27/2018 07:57 PM, Luis R. Rodriguez wrote:
> On Tue, Feb 27, 2018 at 03:49:49PM -0500, Waiman Long wrote:
>> Even with clamped sysctl parameters, it is still not that straight
>> forward to figure out the exact range of those parameters. One may
>> try to write extreme parameter values to see if they get clamped.
>> To make it easier, a warning with the expected range will now be
>> printed in the kernel ring buffer when a clamped sysctl parameter
>> receives an out of range value.
>>
>> Signed-off-by: Waiman Long <longman@redhat.com>
>> ---
>> include/linux/sysctl.h | 1 +
>> kernel/sysctl.c | 55 ++++++++++++++++++++++++++++++++++++++++++--------
>> 2 files changed, 48 insertions(+), 8 deletions(-)
>>
>> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
>> index eceeaee..4e4f74a2 100644
>> --- a/include/linux/sysctl.h
>> +++ b/include/linux/sysctl.h
>> @@ -128,6 +128,7 @@ struct ctl_table
>> * ctl_table flags (16 different flags, at most)
>> */
>> #define CTL_FLAGS_CLAMP_RANGE (1 << 0) /* Clamp to min/max range */
>> +#define CTL_FLAGS_OOR_WARNED (1 << 1) /* Out-of-range warning issued */
> With the enum set you can then kdocify this too.

Yes, will do.

>> struct ctl_node {
>> struct rb_node node;
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index 2b2b30c..f9f3373 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -2515,36 +2515,54 @@ static int proc_dointvec_minmax_sysadmin(struct ctl_table *table, int write,
>> * min: ptr to minimum allowable value
>> * max: ptr to maximum allowable value
>> * flags: ptr to flags
>> + * name: sysctl parameter name
>> */
>> struct do_proc_dointvec_minmax_conv_param {
>> int *min;
>> int *max;
>> uint16_t *flags;
>> + const char *name;
>> };
>>
>> static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
>> int *valp,
>> int write, void *data)
>> {
>> +#define SYSCTL_WARN_MSG \
>> +"Kernel parameter \"%s\" was set out of range [%d, %d], clamped to %d.\n"
> Please loose this define. What about a proc_ctl_warn() which takes the
> parameters and then does the checks?

Yes, I think that is better.

>> +
>> struct do_proc_douintvec_minmax_conv_param *param = data;
>>
>> if (write) {
>> unsigned int val = *lvalp;
>> + bool clamped = false;
>> bool clamp = param->flags &&
>> (*param->flags & CTL_FLAGS_CLAMP_RANGE);
>>
>> @@ -2623,24 +2649,36 @@ static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
>> return -EINVAL;
>>
>> if (param->min && *param->min > val) {
>> - if (clamp)
>> + if (clamp) {
>> val = *param->min;
>> - else
>> + clamped = true;
>> + } else {
>> return -ERANGE;
>> + }
>> }
>> if (param->max && *param->max < val) {
>> - if (clamp)
>> + if (clamp) {
>> val = *param->max;
>> - else
>> + clamped = true;
>> + } else {
>> return -ERANGE;
>> + }
>> }
>> *valp = val;
>> + if (clamped && param->name &&
>> + !(*param->flags & CTL_FLAGS_OOR_WARNED)) {
>> + pr_warn(SYSCTL_WARN_MSG, param->name,
>> + param->min ? *param->min : 0,
>> + param->max ? *param->max : UINT_MAX, val);
>> + *param->flags |= CTL_FLAGS_OOR_WARNED;
> Why not just use pr_warn_once()?
>
> Luis

Right, pr_warn_once can be used in this case.

Cheers,
Longman

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