Re: [PATCH] CVE-2018-19591: if_nametoindex: Fix descriptor for overlong name [BZ #23927]

[Florian Weimer <fweimer at redhat dot com>]

* Andreas Schwab:

> On Nov 27 2018, Florian Weimer <fweimer@redhat.com> wrote:
>
>> diff --git a/sysdeps/unix/sysv/linux/if_index.c b/sysdeps/unix/sysv/linux/if_index.c
>> index e3d08982d9..3e999d6509 100644
>> --- a/sysdeps/unix/sysv/linux/if_index.c
>> +++ b/sysdeps/unix/sysv/linux/if_index.c
>> @@ -45,6 +45,7 @@ __if_nametoindex (const char *ifname)
>>  
>>    if (strlen (ifname) >= IFNAMSIZ)
>>      {
>> +      __close_nocancel_nostatus (fd);
>>        __set_errno (ENODEV);
>>        return 0;
>>      }
>
> Just move it before the opensock call.

Like this?

2018-11-27  Florian Weimer  <fweimer@redhat.com>

	[BZ #23927]
	CVE-2018-19591
	* sysdeps/unix/sysv/linux/if_index.c (__if_nametoindex): Avoid
	descriptor leak in case of ENODEV error.

diff --git a/NEWS b/NEWS
index f488821af1..1098be1afb 100644
--- a/NEWS
+++ b/NEWS
@@ -57,7 +57,9 @@ Changes to build and runtime requirements:
 
 Security related changes:
 
-  [Add security related changes here]
+  CVE-2018-19591: A file descriptor leak in if_nametoindex can lead to a
+  denial of service due to resource exhaustion when processing getaddrinfo
+  calls with crafted host names.  Reported by Guido Vranken.
 
 The following bugs are resolved with this release:
 
diff --git a/sysdeps/unix/sysv/linux/if_index.c b/sysdeps/unix/sysv/linux/if_index.c
index e3d08982d9..782fc5e175 100644
--- a/sysdeps/unix/sysv/linux/if_index.c
+++ b/sysdeps/unix/sysv/linux/if_index.c
@@ -38,11 +38,6 @@ __if_nametoindex (const char *ifname)
   return 0;
 #else
   struct ifreq ifr;
-  int fd = __opensock ();
-
-  if (fd < 0)
-    return 0;
-
   if (strlen (ifname) >= IFNAMSIZ)
     {
       __set_errno (ENODEV);
@@ -50,6 +45,12 @@ __if_nametoindex (const char *ifname)
     }
 
   strncpy (ifr.ifr_name, ifname, sizeof (ifr.ifr_name));
+
+  int fd = __opensock ();
+
+  if (fd < 0)
+    return 0;
+
   if (__ioctl (fd, SIOCGIFINDEX, &ifr) < 0)
     {
       int saved_errno = errno;