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

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

[Wen Yang]

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.

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 do_proc_dointvec_minmax_conv_param {
-	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