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List:       xen-announce
Subject:    [Xen-announce] Xen Security Advisory 68 (CVE-2013-4369) - possible null dereference when parsing vif
From:       Xen.org security team <security () xen ! org>
Date:       2013-10-10 12:22:45
Message-ID: E1VUFGP-0002YX-VB () xenbits ! xen ! org
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             Xen Security Advisory CVE-2013-4369 / XSA-68
                               version 2

     possible null dereference when parsing vif ratelimiting info

UPDATES IN VERSION 2
====================

Public release.

ISSUE DESCRIPTION
=================

The libxlu library function xlu_vif_parse_rate does not properly
handle inputs which consist solely of the '@' character, leading to a
NULL pointer dereference.

IMPACT
======

A toolstack which allows untrusted users to specify an arbitrary
configuration for the VIF rate can be subjected to a DOS.

The only known user of this library is the xl toolstack which does not
have a central long running daemon and therefore the impact is limited
to crashing the process which is creating the domain, which exists
only to service a single domain.

VULNERABLE SYSTEMS
==================

The vulnerable code is present from Xen 4.2 onwards.

MITIGATION
==========

Disallowing untrusted users from specifying arbitrary VIF rate limits
will avoid this issue.

CREDITS
=======

This issue was discovered by Coverity Scan and Matthew Daley.

RESOLUTION
==========

Applying the attached patch resolves this issue in all branches

xsa68.patch        xen-unstable, Xen 4.3.x, Xen 4.2.x

$ sha256sum xsa68*.patch
64716cb49696298e0bbd9556fe9d6f559a4e2785081e28d50607317b6e27ba32  xsa68.patch
$
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["xsa68.patch" (application/octet-stream)]

libxl: fix vif rate parsing

strtok can return NULL here. We don't need to use strtok anyway, so just
use a simple strchr method.

Coverity-ID: 1055642

This is CVE-2013-4369 / XSA-68

Signed-off-by: Matthew Daley <mattjd@gmail.com>

Fix type. Add test case

Signed-off-by: Ian Campbell <Ian.campbell@citrix.com>

diff --git a/tools/libxl/check-xl-vif-parse b/tools/libxl/check-xl-vif-parse
index 0473182..02c6dba 100755
--- a/tools/libxl/check-xl-vif-parse
+++ b/tools/libxl/check-xl-vif-parse
@@ -206,4 +206,8 @@ expected </dev/null
 one $e rate=4294967295GB/s@5us
 one $e rate=4296MB/s@4294s
 
+# test include of single '@'
+expected </dev/null
+one $e rate=@
+
 complete
diff --git a/tools/libxl/libxlu_vif.c b/tools/libxl/libxlu_vif.c
index 3b3de0f..0665e62 100644
--- a/tools/libxl/libxlu_vif.c
+++ b/tools/libxl/libxlu_vif.c
@@ -95,23 +95,30 @@ int xlu_vif_parse_rate(XLU_Config *cfg, const char *rate, libxl_device_nic *nic)
     uint64_t bytes_per_sec = 0;
     uint64_t bytes_per_interval = 0;
     uint32_t interval_usecs = 50000UL; /* Default to 50ms */
-    char *ratetok, *tmprate;
+    char *p, *tmprate;
     int rc = 0;
 
     tmprate = strdup(rate);
+    if (tmprate == NULL) {
+        rc = ENOMEM;
+        goto out;
+    }
+
+    p = strchr(tmprate, '@');
+    if (p != NULL)
+        *p++ = 0;
+
     if (!strcmp(tmprate,"")) {
         xlu__vif_err(cfg, "no rate specified", rate);
         rc = EINVAL;
         goto out;
     }
 
-    ratetok = strtok(tmprate, "@");
-    rc = vif_parse_rate_bytes_per_sec(cfg, ratetok, &bytes_per_sec);
+    rc = vif_parse_rate_bytes_per_sec(cfg, tmprate, &bytes_per_sec);
     if (rc) goto out;
 
-    ratetok = strtok(NULL, "@");
-    if (ratetok != NULL) {
-        rc = vif_parse_rate_interval_usecs(cfg, ratetok, &interval_usecs);
+    if (p != NULL) {
+        rc = vif_parse_rate_interval_usecs(cfg, p, &interval_usecs);
         if (rc) goto out;
     }
 


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