sysctl: make sure to terminate strings with a NUL

This is a slightly more complete fix for the previous minimal sysctl
string fix.  It always terminates the returned string with a NUL, even
if the full result wouldn't fit in the user-supplied buffer.

The returned length is the full untruncated length, so that you can
tell when truncation has occurred.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 15 insertions, 10 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index e5102ea6e104..b53115b882e1 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2192,27 +2192,32 @@ int sysctl_string(ctl_table *table, int __user *name, int nlen,
                   void __user *oldval, size_t __user *oldlenp,
                   void __user *newval, size_t newlen, void **context)
 {
-        size_t l, len;
-        
         if (!table->data || !table->maxlen) 
                 return -ENOTDIR;
         
         if (oldval && oldlenp) {
-                if (get_user(len, oldlenp))
+                size_t bufsize;
+                if (get_user(bufsize, oldlenp))
                         return -EFAULT;
-                if (len) {
-                        l = strlen(table->data)+1;
-                        if (len > l) len = l;
-                        if (len >= table->maxlen)
+                if (bufsize) {
+                        size_t len = strlen(table->data), copied;
+
+                        /* This shouldn't trigger for a well-formed sysctl */
+                        if (len > table->maxlen)
                                 len = table->maxlen;
-                        if(copy_to_user(oldval, table->data, len))
+
+                        /* Copy up to a max of bufsize-1 bytes of the string */
+                        copied = (len >= bufsize) ? bufsize - 1 : len;
+
+                        if (copy_to_user(oldval, table->data, copied) ||
+                            put_user(0, (char __user *)(oldval + copied)))
                                 return -EFAULT;
-                        if(put_user(len, oldlenp))
+                        if (put_user(len, oldlenp))
                                 return -EFAULT;
                 }
         }
         if (newval && newlen) {
-                len = newlen;
+                size_t len = newlen;
                 if (len > table->maxlen)
                         len = table->maxlen;
                 if(copy_from_user(table->data, newval, len))