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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@redhat.com>
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>