[PATCH 1/3] sysctl: Add range clamping intvec helper functions

[Waiman Long <longman@redhat.com>]

The current intvec range helper functions will fail with error when
users try to assign an out-of-range value.

The following new non-failing range helper functions are now added:
 - proc_dointvec_clamp_minmax()
 - proc_douintvec_clamp_minmax()

The new helper functions will clamp the value to within the given
min/max range without failing it.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 include/linux/sysctl.h |  6 ++++
 kernel/sysctl.c        | 97 ++++++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 96 insertions(+), 7 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index b769ecf..7684ea5 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -63,6 +63,12 @@ extern int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int,
 				      void __user *, size_t *, loff_t *);
 extern int proc_do_large_bitmap(struct ctl_table *, int,
 				void __user *, size_t *, loff_t *);
+extern int proc_dointvec_clamp_minmax(struct ctl_table *table, int write,
+				      void __user *buffer, size_t *lenp,
+				      loff_t *ppos);
+extern int proc_douintvec_clamp_minmax(struct ctl_table *table, int write,
+				       void __user *buffer, size_t *lenp,
+				       loff_t *ppos);
 
 /*
  * Register a set of sysctl names by calling register_sysctl_table
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index f98f28c..f86c3a7 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2500,9 +2500,15 @@ static int proc_dointvec_minmax_sysadmin(struct ctl_table *table, int write,
 }
 #endif
 
+/*
+ * The clamping flag, if set, will clamp the input value to the range
+ * specified by the given min/max values instead of returning error when
+ * out of range.
+ */
 struct do_proc_dointvec_minmax_conv_param {
 	int *min;
 	int *max;
+	bool clamp;
 };
 
 static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
@@ -2512,9 +2518,18 @@ static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
 	struct do_proc_dointvec_minmax_conv_param *param = data;
 	if (write) {
 		int val = *negp ? -*lvalp : *lvalp;
-		if ((param->min && *param->min > val) ||
-		    (param->max && *param->max < val))
-			return -EINVAL;
+		if (param->min && *param->min > val) {
+			if (param->clamp)
+				val = *param->min;
+			else
+				return -EINVAL;
+		}
+		if (param->max && *param->max < val) {
+			if (param->clamp)
+				val = *param->max;
+			else
+				return -EINVAL;
+		}
 		*valp = val;
 	} else {
 		int val = *valp;
@@ -2556,9 +2571,38 @@ int proc_dointvec_minmax(struct ctl_table *table, int write,
 				do_proc_dointvec_minmax_conv, &param);
 }
 
+/**
+ * proc_dointvec_clamp_minmax - read a vector of integers with min/max values
+ * @table: the sysctl table
+ * @write: %TRUE if this is a write to the sysctl file
+ * @buffer: the user buffer
+ * @lenp: the size of the user buffer
+ * @ppos: file position
+ *
+ * Reads/writes up to table->maxlen/sizeof(unsigned int) integer
+ * values from/to the user buffer, treated as an ASCII string.
+ *
+ * This routine will clamp the values to within the range specified by
+ * table->extra1 (min) and table->extra2 (max).
+ *
+ * Returns 0 on success.
+ */
+int proc_dointvec_clamp_minmax(struct ctl_table *table, int write,
+		  void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct do_proc_dointvec_minmax_conv_param param = {
+		.min = (int *) table->extra1,
+		.max = (int *) table->extra2,
+		.clamp = true,
+	};
+	return do_proc_dointvec(table, write, buffer, lenp, ppos,
+				do_proc_dointvec_minmax_conv, &param);
+}
+
 struct do_proc_douintvec_minmax_conv_param {
 	unsigned int *min;
 	unsigned int *max;
+	bool clamp;
 };
 
 static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
@@ -2573,10 +2617,18 @@ static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
 		if (*lvalp > UINT_MAX)
 			return -EINVAL;
 
-		if ((param->min && *param->min > val) ||
-		    (param->max && *param->max < val))
-			return -ERANGE;
-
+		if (param->min && *param->min > val) {
+			if (param->clamp)
+				val = *param->min;
+			else
+				return -ERANGE;
+		}
+		if (param->max && *param->max < val) {
+			if (param->clamp)
+				val = *param->max;
+			else
+				return -ERANGE;
+		}
 		*valp = val;
 	} else {
 		unsigned int val = *valp;
@@ -2616,6 +2668,37 @@ int proc_douintvec_minmax(struct ctl_table *table, int write,
 				 do_proc_douintvec_minmax_conv, &param);
 }
 
+/**
+ * proc_douintvec_clamp_minmax - read a vector of uints with min/max values
+ * @table: the sysctl table
+ * @write: %TRUE if this is a write to the sysctl file
+ * @buffer: the user buffer
+ * @lenp: the size of the user buffer
+ * @ppos: file position
+ *
+ * Reads/writes up to table->maxlen/sizeof(unsigned int) unsigned integer
+ * values from/to the user buffer, treated as an ASCII string. Negative
+ * strings are not allowed.
+ *
+ * This routine will clamp the values to within the range specified by
+ * table->extra1 (min) and table->extra2 (max). There is a final sanity
+ * check for UINT_MAX to avoid having to support wrap around uses from
+ * userspace.
+ *
+ * Returns 0 on success.
+ */
+int proc_douintvec_clamp_minmax(struct ctl_table *table, int write,
+			  void __user *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,
+		.clamp = true,
+	};
+	return do_proc_douintvec(table, write, buffer, lenp, ppos,
+				 do_proc_douintvec_minmax_conv, &param);
+}
+
 static int do_proc_dopipe_max_size_conv(unsigned long *lvalp,
 					unsigned int *valp,
 					int write, void *data)
-- 
1.8.3.1