libxl: Fix possible invalid read

According to the following valgrind output, there seems to be a
invalid limit for the iterator (captured on Fedora 19):

==3945== Invalid read of size 1
==3945==    at 0x1E1FA410: libxlVmStart (libxl_driver.c:475)
==3945==    by 0x1E1FAD9A: libxlDomainCreateWithFlags (libxl_driver.c:2633)
==3945==    by 0x5187D46: virDomainCreate (libvirt.c:9439)
==3945==    by 0x13BAA6: remoteDispatchDomainCreateHelper (remote_dispatch.h:2910)
==3945==    by 0x51DE5B9: virNetServerProgramDispatch (virnetserverprogram.c:435)
==3945==    by 0x51D93E7: virNetServerHandleJob (virnetserver.c:165)
==3945==    by 0x50F5BF4: virThreadPoolWorker (virthreadpool.c:144)
==3945==    by 0x50F5670: virThreadHelper (virthreadpthread.c:161)
==3945==    by 0x8046C52: start_thread (pthread_create.c:308)
==3945==    by 0x8758E1C: clone (clone.S:113)
==3945==  Address 0x23424d81 is 0 bytes after a block of size 1 alloc'd
==3945==    at 0x4A08121: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==3945==    by 0x50B1F8C: virAllocN (viralloc.c:189)
==3945==    by 0x1E1FA3CA: libxlVmStart (libxl_driver.c:468)
==3945==    by 0x1E1FAD9A: libxlDomainCreateWithFlags (libxl_driver.c:2633)
==3945==    by 0x5187D46: virDomainCreate (libvirt.c:9439)
==3945==    by 0x13BAA6: remoteDispatchDomainCreateHelper (remote_dispatch.h:2910)
==3945==    by 0x51DE5B9: virNetServerProgramDispatch (virnetserverprogram.c:435)
==3945==    by 0x51D93E7: virNetServerHandleJob (virnetserver.c:165)
==3945==    by 0x50F5BF4: virThreadPoolWorker (virthreadpool.c:144)
==3945==    by 0x50F5670: virThreadHelper (virthreadpthread.c:161)
==3945==    by 0x8046C52: start_thread (pthread_create.c:308)
==3945==    by 0x8758E1C: clone (clone.S:113)
==3945==

Related: https://bugzilla.redhat.com/show_bug.cgi?id=1013045Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

src/libxl/libxl_driver.c

@@ -454,6 +454,7 @@ libxlDomainSetVcpuAffinities(libxlDriverPrivatePtr driver, virDomainObjPtr vm)
     size_t cpumaplen;
     int vcpu;
     size_t i;
+    size_t limit;
     int ret = -1;
 
     if (libxlDoNodeGetInfo(driver, &nodeinfo) < 0)
@@ -470,7 +471,8 @@ libxlDomainSetVcpuAffinities(libxlDriverPrivatePtr driver, virDomainObjPtr vm)
 
         cpumask = (uint8_t*) def->cputune.vcpupin[vcpu]->cpumask;
 
-        for (i = 0; i < VIR_DOMAIN_CPUMASK_LEN; ++i) {
+        limit = MIN(VIR_DOMAIN_CPUMASK_LEN, cpumaplen);
+        for (i = 0; i < limit; ++i) {
             if (cpumask[i])
                 VIR_USE_CPU(cpumap, i);
         }