Re: [RESEND PATCH v4] sysctl: simplify the min/max boundary check

[Wen Yang <wen.yang@linux.dev>]

On 2024/12/18 22:11, Joel Granados wrote:
> On Sun, Dec 01, 2024 at 10:00:58PM +0800, Wen Yang wrote:
>> The do_proc_dointvec_minmax_conv_param structure provides the minimum and
>> maximum values for doing range checking for the proc_dointvec_minmax()
>> handler, however min/max is a pointer and may be NULL, so the following
>> code snippet appears multiple times:
>>          if ((param->min && *param->min > tmp) ||
>>              (param->max && *param->max < tmp))
>>
>> And int types also have min/max values, so when the pointer is NULL,
>> explicitly setting min/max to INT_{MIN/MAX} could simplify the code a bit.
> Sorry, but this does not make sense to me. This simplification is way
> too small and it seems that it is just being done for the sake of it.
> Additionally, by giving these min/max values you are potentially
> changing the behaviour of existing calls, which is concerning for
> such a small change/gain.
> 

Thanks for your comments.

The implementation of do_proc_dointvec_conv() utilizes the default range 
of the int type, while do_proc_dointvec_minmax_conv() additionally 
utilizes min/max pointers, which are actually table->extra {1,2} 
pointers passed in.

If we can dereference the table->extra {1,2} pointers to numerical 
values in advance (such as the modification here), we can take advantage 
of memory locality and improve performance a bit.

If the current simplification is too small, we could further improve it, 
such as considering do_proc_minmax_conv_param, 
do_proc_minmax_conv_param, do_proc_dointvec_minmax_conv, 
do_proc_douintvec_conv, do_proc_douintvec_minmax_conv , etc.

All of this is in preparation for ultimately killing the table 
->{extra1, extra2} pointers.

We will rework later and send v5.

--
Best wishes，
Wen


> Thx for the contribution but will stay with the pointers for now.
> 
> Best
> 
>>
>> Similar changes were also made for do_proc_douintvec_minmax_conv_param.
>>
>> Signed-off-by: Wen Yang <wen.yang@linux.dev>
>> Cc: Joel Granados <joel.granados@kernel.org>
>> Cc: Luis Chamberlain <mcgrof@kernel.org>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: Eric W. Biederman <ebiederm@xmission.com>
>> Cc: Christian Brauner <brauner@kernel.org>
>> Cc: Dave Young <dyoung@redhat.com>
>> Cc: linux-kernel@vger.kernel.org
>> ---
>>   kernel/sysctl.c | 75 ++++++++++++++++++++++---------------------------
>>   1 file changed, 34 insertions(+), 41 deletions(-)
>>
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index 79e6cb1d5c48..47e2fe4fe978 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -810,16 +810,16 @@ static int proc_taint(const struct ctl_table *table, int write,
>>   
>>   /**
>>    * struct do_proc_dointvec_minmax_conv_param - proc_dointvec_minmax() range checking structure
>> - * @min: pointer to minimum allowable value
>> - * @max: pointer to maximum allowable value
>> + * @min: the minimum allowable value
>> + * @max: the maximum allowable value
>>    *
>>    * The do_proc_dointvec_minmax_conv_param structure provides the
>>    * minimum and maximum values for doing range checking for those sysctl
>> - * parameters that use the proc_dointvec_minmax() handler.
>> + * parameters that use the proc_dointvec_minmax(), proc_dou8vec_minmax() and so on.
>>    */
>>   struct ram {
>> -	int *min;
>> -	int *max;
>> +	int min;
>> +	int max;
>>   };
>>   
>>   static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
>> @@ -839,8 +839,7 @@ static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
>>   		return ret;
>>   
>>   	if (write) {
>> -		if ((param->min && *param->min > tmp) ||
>> -		    (param->max && *param->max < tmp))
>> +		if ((param->min > tmp) || (param->max < tmp))
>>   			return -EINVAL;
>>   		WRITE_ONCE(*valp, tmp);
>>   	}
>> @@ -867,26 +866,26 @@ static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
>>   int proc_dointvec_minmax(const struct ctl_table *table, int write,
>>   		  void *buffer, size_t *lenp, loff_t *ppos)
>>   {
>> -	struct do_proc_dointvec_minmax_conv_param param = {
>> -		.min = (int *) table->extra1,
>> -		.max = (int *) table->extra2,
>> -	};
>> +	struct do_proc_dointvec_minmax_conv_param param;
>> +
>> +	param.min = (table->extra1) ? *(int *) table->extra1 : INT_MIN;
>> +	param.max = (table->extra2) ? *(int *) table->extra2 : INT_MAX;
>>   	return do_proc_dointvec(table, write, buffer, lenp, ppos,
>>   				do_proc_dointvec_minmax_conv, &param);
>>   }
>>   
>>   /**
>>    * struct do_proc_douintvec_minmax_conv_param - proc_douintvec_minmax() range checking structure
>> - * @min: pointer to minimum allowable value
>> - * @max: pointer to maximum allowable value
>> + * @min: minimum allowable value
>> + * @max: maximum allowable value
>>    *
>>    * The do_proc_douintvec_minmax_conv_param structure provides the
>>    * minimum and maximum values for doing range checking for those sysctl
>>    * parameters that use the proc_douintvec_minmax() handler.
>>    */
>>   struct do_proc_douintvec_minmax_conv_param {
>> -	unsigned int *min;
>> -	unsigned int *max;
>> +	unsigned int min;
>> +	unsigned int max;
>>   };
>>   
>>   static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
>> @@ -904,8 +903,7 @@ static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
>>   		return ret;
>>   
>>   	if (write) {
>> -		if ((param->min && *param->min > tmp) ||
>> -		    (param->max && *param->max < tmp))
>> +		if ((param->min > tmp) || (param->max < tmp))
>>   			return -ERANGE;
>>   
>>   		WRITE_ONCE(*valp, tmp);
>> @@ -936,10 +934,11 @@ static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
>>   int proc_douintvec_minmax(const struct ctl_table *table, int write,
>>   			  void *buffer, size_t *lenp, loff_t *ppos)
>>   {
>> -	struct do_proc_douintvec_minmax_conv_param param = {
>> -		.min = (unsigned int *) table->extra1,
>> -		.max = (unsigned int *) table->extra2,
>> -	};
>> +	struct do_proc_douintvec_minmax_conv_param param;
>> +
>> +	param.min = (table->extra1) ? *(unsigned int *) table->extra1 : 0;
>> +	param.max = (table->extra2) ? *(unsigned int *) table->extra2 : UINT_MAX;
>> +
>>   	return do_proc_douintvec(table, write, buffer, lenp, ppos,
>>   				 do_proc_douintvec_minmax_conv, &param);
>>   }
>> @@ -965,23 +964,17 @@ int proc_dou8vec_minmax(const struct ctl_table *table, int write,
>>   			void *buffer, size_t *lenp, loff_t *ppos)
>>   {
>>   	struct ctl_table tmp;
>> -	unsigned int min = 0, max = 255U, val;
>> +	unsigned int val;
>>   	u8 *data = table->data;
>> -	struct do_proc_douintvec_minmax_conv_param param = {
>> -		.min = &min,
>> -		.max = &max,
>> -	};
>> +	struct do_proc_douintvec_minmax_conv_param param;
>>   	int res;
>>   
>>   	/* Do not support arrays yet. */
>>   	if (table->maxlen != sizeof(u8))
>>   		return -EINVAL;
>>   
>> -	if (table->extra1)
>> -		min = *(unsigned int *) table->extra1;
>> -	if (table->extra2)
>> -		max = *(unsigned int *) table->extra2;
>> -
>> +	param.min = (table->extra1) ? *(unsigned int *) table->extra1 : 0;
>> +	param.max = (table->extra2) ? *(unsigned int *) table->extra2 : 255U;
>>   	tmp = *table;
>>   
>>   	tmp.maxlen = sizeof(val);
>> @@ -1022,7 +1015,7 @@ static int __do_proc_doulongvec_minmax(void *data,
>>   		void *buffer, size_t *lenp, loff_t *ppos,
>>   		unsigned long convmul, unsigned long convdiv)
>>   {
>> -	unsigned long *i, *min, *max;
>> +	unsigned long *i, min, max;
>>   	int vleft, first = 1, err = 0;
>>   	size_t left;
>>   	char *p;
>> @@ -1033,8 +1026,9 @@ static int __do_proc_doulongvec_minmax(void *data,
>>   	}
>>   
>>   	i = data;
>> -	min = table->extra1;
>> -	max = table->extra2;
>> +	min = (table->extra1) ? *(unsigned long *) table->extra1 : 0;
>> +	max = (table->extra2) ? *(unsigned long *) table->extra2 : ULONG_MAX;
>> +
>>   	vleft = table->maxlen / sizeof(unsigned long);
>>   	left = *lenp;
>>   
>> @@ -1066,7 +1060,7 @@ static int __do_proc_doulongvec_minmax(void *data,
>>   			}
>>   
>>   			val = convmul * val / convdiv;
>> -			if ((min && val < *min) || (max && val > *max)) {
>> +			if ((val < min) || (val > max)) {
>>   				err = -EINVAL;
>>   				break;
>>   			}
>> @@ -1236,8 +1230,7 @@ static int do_proc_dointvec_ms_jiffies_minmax_conv(bool *negp, unsigned long *lv
>>   		return ret;
>>   
>>   	if (write) {
>> -		if ((param->min && *param->min > tmp) ||
>> -				(param->max && *param->max < tmp))
>> +		if ((param->min > tmp) || (param->max < tmp))
>>   			return -EINVAL;
>>   		*valp = tmp;
>>   	}
>> @@ -1269,10 +1262,10 @@ int proc_dointvec_jiffies(const struct ctl_table *table, int write,
>>   int proc_dointvec_ms_jiffies_minmax(const struct ctl_table *table, int write,
>>   			  void *buffer, size_t *lenp, loff_t *ppos)
>>   {
>> -	struct do_proc_dointvec_minmax_conv_param param = {
>> -		.min = (int *) table->extra1,
>> -		.max = (int *) table->extra2,
>> -	};
>> +	struct do_proc_dointvec_minmax_conv_param param;
>> +
>> +	param.min = (table->extra1) ? *(int *) table->extra1 : INT_MIN;
>> +	param.max = (table->extra2) ? *(int *) table->extra2 : INT_MAX;
>>   	return do_proc_dointvec(table, write, buffer, lenp, ppos,
>>   			do_proc_dointvec_ms_jiffies_minmax_conv, &param);
>>   }
>> -- 
>> 2.25.1
>>
>