sysctl: Factor out sysctl_data.

There as been no easy way to wrap the default sysctl strategy routine except
for returning 0.  Which is not always what we want.  The few instances I have
seen that want different behaviour have written their own version of
sysctl_data.  While not too hard it is unnecessary code and has the potential
for extra bugs.

So to make these situations easier and make that part of sysctl more symetric
I have factord sysctl_data out of do_sysctl_strategy and exported as a
function everyone can use.

Further having sysctl_data be an explicit function makes checking for badly
formed sysctl tables much easier.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Alexey Dobriyan <adobriyan@sw.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/sysctl.h

@@ -972,6 +972,7 @@ extern int do_sysctl_strategy (struct ctl_table *table,
 			       void __user *oldval, size_t __user *oldlenp,
 			       void __user *newval, size_t newlen);
 
+extern ctl_handler sysctl_data;
 extern ctl_handler sysctl_string;
 extern ctl_handler sysctl_intvec;
 extern ctl_handler sysctl_jiffies;

kernel/sysctl.c

@@ -1443,7 +1443,6 @@ int do_sysctl_strategy (struct ctl_table *table,
 			void __user *newval, size_t newlen)
 {
 	int op = 0, rc;
-	size_t len;
 
 	if (oldval)
 		op |= 004;
@@ -1464,25 +1463,10 @@ int do_sysctl_strategy (struct ctl_table *table,
 	/* If there is no strategy routine, or if the strategy returns
 	 * zero, proceed with automatic r/w */
 	if (table->data && table->maxlen) {
-		if (oldval && oldlenp) {
+		rc = sysctl_data(table, name, nlen, oldval, oldlenp,
-			if (get_user(len, oldlenp))
+				 newval, newlen);
-				return -EFAULT;
+		if (rc < 0)
-			if (len) {
+			return rc;
-				if (len > table->maxlen)
-					len = table->maxlen;
-				if(copy_to_user(oldval, table->data, len))
-					return -EFAULT;
-				if(put_user(len, oldlenp))
-					return -EFAULT;
-			}
-		}
-		if (newval && newlen) {
-			len = newlen;
-			if (len > table->maxlen)
-				len = table->maxlen;
-			if(copy_from_user(table->data, newval, len))
-				return -EFAULT;
-		}
 	}
 	return 0;
 }
@@ -2381,6 +2365,40 @@ int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int write,
  * General sysctl support routines 
  */
 
+/* The generic sysctl data routine (used if no strategy routine supplied) */
+int sysctl_data(struct ctl_table *table, int __user *name, int nlen,
+		void __user *oldval, size_t __user *oldlenp,
+		void __user *newval, size_t newlen)
+{
+	size_t len;
+
+	/* Get out of I don't have a variable */
+	if (!table->data || !table->maxlen)
+		return -ENOTDIR;
+
+	if (oldval && oldlenp) {
+		if (get_user(len, oldlenp))
+			return -EFAULT;
+		if (len) {
+			if (len > table->maxlen)
+				len = table->maxlen;
+			if (copy_to_user(oldval, table->data, len))
+				return -EFAULT;
+			if (put_user(len, oldlenp))
+				return -EFAULT;
+		}
+	}
+
+	if (newval && newlen) {
+		if (newlen > table->maxlen)
+			newlen = table->maxlen;
+
+		if (copy_from_user(table->data, newval, newlen))
+			return -EFAULT;
+	}
+	return 1;
+}
+
 /* The generic string strategy routine: */
 int sysctl_string(struct ctl_table *table, int __user *name, int nlen,
 		  void __user *oldval, size_t __user *oldlenp,
@@ -2569,6 +2587,13 @@ out:
 	return -ENOSYS;
 }
 
+int sysctl_data(struct ctl_table *table, int __user *name, int nlen,
+		  void __user *oldval, size_t __user *oldlenp,
+		  void __user *newval, size_t newlen)
+{
+	return -ENOSYS;
+}
+
 int sysctl_string(struct ctl_table *table, int __user *name, int nlen,
 		  void __user *oldval, size_t __user *oldlenp,
 		  void __user *newval, size_t newlen)
@@ -2616,4 +2641,5 @@ EXPORT_SYMBOL(sysctl_intvec);
 EXPORT_SYMBOL(sysctl_jiffies);
 EXPORT_SYMBOL(sysctl_ms_jiffies);
 EXPORT_SYMBOL(sysctl_string);
+EXPORT_SYMBOL(sysctl_data);
 EXPORT_SYMBOL(unregister_sysctl_table);