[libvirt] [PATCH] domtop: Properly free cpu status

Michal Privoznik mprivozn at redhat.com
Mon Apr 20 09:41:37 UTC 2015

So, in the example the cpu stats are collected within a function
called do_top. At the beginning of the function we ask the daemon for
how much vCPUs can we get stats, and how many stats for a vCPU can we
get. This is because it's how our API works - users are required to
preallocate a chunk of memory for the results. Now, at the end, we try
to free the allocated array, but we are not doing it correctly.
There's this virTypedParamsFree() function which gets a pointer to the
array and the length of the array. However, if there was an error in
getting vCPU stats we pass a negative number instead of the originally
computed value. This flaw results in SIGSEGV:

libvirt: QEMU Driver error : Requested operation is not valid: domain is not running
ERROR do_top:333 : Unable to get cpu stats
==29201== Invalid read of size 4
==29201==    at 0x4F1DF8B: virTypedParamsClear (virtypedparam.c:1145)
==29201==    by 0x4F1DFEB: virTypedParamsFree (virtypedparam.c:1165)
==29201==    by 0x4023C3: do_top (domtop.c:349)
==29201==    by 0x40260B: main (domtop.c:386)
==29201==  Address 0x131cd7c0 is 16 bytes after a block of size 768 alloc'd
==29201==    at 0x4C2C070: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==29201==    by 0x401FF1: do_top (domtop.c:295)
==29201==    by 0x40260B: main (domtop.c:386)

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
 examples/domtop/domtop.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/examples/domtop/domtop.c b/examples/domtop/domtop.c
index e50988e..2283994 100644
--- a/examples/domtop/domtop.c
+++ b/examples/domtop/domtop.c
@@ -346,8 +346,8 @@ do_top(virConnectPtr conn,
     ret = 0;
-    virTypedParamsFree(now_params, now_nparams * max_id);
-    virTypedParamsFree(then_params, then_nparams * max_id);
+    virTypedParamsFree(now_params, nparams * max_id);
+    virTypedParamsFree(then_params, nparams * max_id);
     if (dom)
     return ret;

More information about the libvir-list mailing list