conf: Fix libvirtd crash and memory leak caused by virDomainVcpuPinDel()

The function virDomainVcpuPinDel() used vcpupin_list to stand for
def->cputune.vcpupin, which made the codes more readable.
However, in this function, it will realloc vcpupin_list later.
As the definition of realloc(), it may free vcpupin_list and then
points it to a new-realloced address, but def->cputune.vcpupin doesn't
point to the new address(it's freed however).
Thus,
1) When we refer to the def->cputune.vcpupin afterwards, which was freed
by realloc(), an INVALID READ occurs, and libvirtd may crash.
2) As no one will use vcpupin_list any more, and no one frees it(it's just
alloced by realloc()), memory leak occurs.

Part of the valgrind logs are shown as below:
==1837== Thread 15:
==1837== Invalid read of size 8
==1837==    at 0x5367337: virDomainDefFormatInternal (domain_conf.c:18392)
        which is : virBufferAsprintf(buf, "<vcpupin vcpu='%u' ",
                          def->cputune.vcpupin[i]->vcpuid);
==1837==    by 0x536966C: virDomainObjFormat (domain_conf.c:18970)
==1837==    by 0x5369743: virDomainSaveStatus (domain_conf.c:19166)
==1837==    by 0x117B26DC: qemuDomainPinVcpuFlags (qemu_driver.c:4586)
==1837==    by 0x53EA313: virDomainPinVcpuFlags (libvirt.c:9803)
==1837==    by 0x14CB7D: remoteDispatchDomainPinVcpuFlags (remote_dispatch.h:6762)
==1837==    by 0x14CC81: remoteDispatchDomainPinVcpuFlagsHelper (remote_dispatch.h:6740)
==1837==    by 0x5464C30: virNetServerProgramDispatchCall (virnetserverprogram.c:437)
==1837==    by 0x546507A: virNetServerProgramDispatch (virnetserverprogram.c:307)
==1837==    by 0x171B83: virNetServerProcessMsg (virnetserver.c:172)
==1837==    by 0x171E6E: virNetServerHandleJob (virnetserver.c:193)
==1837==    by 0x5318E78: virThreadPoolWorker (virthreadpool.c:145)
==1837==  Address 0x12ea2870 is 0 bytes inside a block of size 16 free'd
==1837==    at 0x4C291AC: realloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==1837==    by 0x52A3D14: virReallocN (viralloc.c:245)
==1837==    by 0x52A3DFB: virShrinkN (viralloc.c:372)
==1837==    by 0x52A3F57: virDeleteElementsN (viralloc.c:503)
==1837==    by 0x533939E: virDomainVcpuPinDel (domain_conf.c:15405)  //doReset为true时才会进到。
==1837==    by 0x117B2642: qemuDomainPinVcpuFlags (qemu_driver.c:4573)
==1837==    by 0x53EA313: virDomainPinVcpuFlags (libvirt.c:9803)
==1837==    by 0x14CB7D: remoteDispatchDomainPinVcpuFlags (remote_dispatch.h:6762)
==1837==    by 0x14CC81: remoteDispatchDomainPinVcpuFlagsHelper (remote_dispatch.h:6740)
==1837==    by 0x5464C30: virNetServerProgramDispatchCall (virnetserverprogram.c:437)
==1837==    by 0x546507A: virNetServerProgramDispatch (virnetserverprogram.c:307)
==1837==    by 0x171B83: virNetServerProcessMsg (virnetserver.c:172)

Steps to reproduce the problem:
1) use virDomainPinVcpuFlags() to pin a guest's vcpu to all the pcpus
of the host.

This patch uses def->cputune.vcpupin instead of vcpupin_list to do the
realloc() job, to avoid invalid read or memory leaking.
Signed-off-by: NZhang Bo <oscar.zhangbo@huawei.com>
Signed-off-by: Yue Wenyuan <yuewenyuan@huawei.com@huawei.com>

src/conf/domain_conf.c

@@ -16453,7 +16453,7 @@ virDomainVcpuPinDel(virDomainDefPtr def, int vcpu)
         if (vcpupin_list[n]->vcpuid == vcpu) {
             virBitmapFree(vcpupin_list[n]->cpumask);
             VIR_FREE(vcpupin_list[n]);
-            VIR_DELETE_ELEMENT(vcpupin_list, n, def->cputune.nvcpupin);
+            VIR_DELETE_ELEMENT(def->cputune.vcpupin, n, def->cputune.nvcpupin);
             return;
         }
     }