Fix possible stack overflow in option parsing routine

It is possible to create a stack overflow by giving an option that is
longer than the buffer that is used during option parsing because the
length of the input string is not checked.

Prevent the issue by always checking the input string length and
discarding options that does not fit in the buffer as invalid.

This issue has been assigned CVE-2017-12481.

Thanks to Gwan Yeong Kim for reporting this issue.

Fixes #1222

1 files changed, 5 insertions, 0 deletions

diff --git a/src/option.cc b/src/option.cc
index ab6c37e0..81f9af5b 100644
--- a/src/option.cc
+++ b/src/option.cc
@@ -42,6 +42,11 @@ namespace {
   {
     char buf[128];
     char * p = buf;
+
+    if (name.length() > 127) {
+        throw_(option_error, _f("Illegal option --%1%") % name);
+    }
+
     foreach (char ch, name) {
       if (ch == '-')
         *p++ = '_';