perf record: Fix failed memory allocation for get_cpuid_str

In x86 architecture dependend part function get_cpuid_str() mallocs a
128 byte buffer, but does not check if the memory allocation succeeded
or not.

When the memory allocation fails, function __get_cpuid() is called with
first parameter being a NULL pointer.  However this function references
its first parameter and operates on a NULL pointer which might cause
core dumps.
Signed-off-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: http://lkml.kernel.org/r/20180117131611.34319-1-tmricht@linux.vnet.ibm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/arch/x86/util/header.c

@@ -70,7 +70,7 @@ get_cpuid_str(struct perf_pmu *pmu __maybe_unused)
 {
 	char *buf = malloc(128);
 
-	if (__get_cpuid(buf, 128, "%s-%u-%X$") < 0) {
+	if (buf && __get_cpuid(buf, 128, "%s-%u-%X$") < 0) {
 		free(buf);
 		return NULL;
 	}