qemu_namespace: Don't leak memory in qemuDomainGetPreservedMounts()

The aim of qemuDomainGetPreservedMounts() is to get a list of
filesystems mounted under /dev and optionally generate a path for
each one where they are moved temporarily when building the
namespace. And the function tries to be a bit clever about it.
For instance, if /dev/shm mount point exists, there's no need to
consider /dev/shm/a nor /dev/shm/b as preserving just 'top level'
/dev/shm gives the same result. To achieve this, the function
iterates over the list of filesystem as returned by
virFileGetMountSubtree() and removes the nested ones. However, it
does so in a bit clumsy way: plain VIR_DELETE_ELEMENT() is used
without freeing the string itself. Therefore, if all three
aforementioned example paths appeared on the list, /dev/shm/a and
/dev/shm/b strings would be leaked.

And when I think about it more, there's no real need to shrink
the array down (realloc()). It's going to be free()-d when
returning from the function. Switch to
VIR_DELETE_ELEMENT_INPLACE() then.

Fixes: cdd9205dfffa3aaed935446a41f0d2dd1357c268
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/qemu/qemu_namespace.c

@@ -159,7 +159,8 @@ qemuDomainGetPreservedMounts(virQEMUDriverConfig *cfg,
 
             if (c && (*c == '/' || *c == '\0')) {
                 VIR_DEBUG("Dropping path %s because of %s", mounts[j], mounts[i]);
-                VIR_DELETE_ELEMENT(mounts, j, nmounts);
+                VIR_FREE(mounts[j]);
+                VIR_DELETE_ELEMENT_INPLACE(mounts, j, nmounts);
             } else {
                 j++;
             }