[glib] g_hostname_is_ip_address: detect integer overflow

[Simon McVittie <smcv src gnome org>]

commit 4496ef91b58bf8895ea04d0aef30a76b44263d6f
Author: Simon McVittie <smcv debian org>
Date:   Fri Dec 2 10:13:00 2016 +0000

    g_hostname_is_ip_address: detect integer overflow
    
    Signed integer overflow is undefined behaviour, which the undefined
    behaviour sanitizer detects.
    
    Previously, if the compiler had implemented this in the obvious way
    (overflowing signed multiplication wraps around mod 2**32), we would
    have incorrectly classified addresses where one octet was, for example,
    (2**32 + 42) as valid IP addresses, by treating that octet as though
    it was 42.
    
    Signed-off-by: Simon McVittie <smcv debian org>
    Bug: https://bugzilla.gnome.org/show_bug.cgi?id=775510
    Reviewed-by: Colin Walters

 glib/ghostutils.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/glib/ghostutils.c b/glib/ghostutils.c
index 79e9514..4be59f7 100644
--- a/glib/ghostutils.c
+++ b/glib/ghostutils.c
@@ -785,7 +785,12 @@ g_hostname_is_ip_address (const gchar *hostname)
       else
         {
           for (end = p; g_ascii_isdigit (*end); end++)
-            octet = 10 * octet + (*end - '0');
+            {
+              octet = 10 * octet + (*end - '0');
+
+              if (octet > 255)
+                break;
+            }
         }
       if (end == p || end > p + 3 || octet > 255)
         return FALSE;