sysctl: don't overflow the user-supplied buffer with '\0'

If the string was too long to fit in the user-supplied buffer,
the sysctl layer would zero-terminate it by writing past the
end of the buffer. Don't do that.

Noticed by Yi Yang <yang.y.yi@gmail.com>

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

1 files changed, 1 insertions, 3 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 9990e10192e8..ad0425a8f709 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2201,14 +2201,12 @@ int sysctl_string(ctl_table *table, int __user *name, int nlen,
                 if (get_user(len, oldlenp))
                         return -EFAULT;
                 if (len) {
-                        l = strlen(table->data);
+                        l = strlen(table->data)+1;
                         if (len > l) len = l;
                         if (len >= table->maxlen)
                                 len = table->maxlen;
                         if(copy_to_user(oldval, table->data, len))
                                 return -EFAULT;
-                        if(put_user(0, ((char __user *) oldval) + len))
-                                return -EFAULT;
                         if(put_user(len, oldlenp))
                                 return -EFAULT;
                 }