perf machine: Pass buffer size to machine__mmap_name

Don't blindly assume that the size of the buffer is enough, use
snprintf.

Cc: Avi Kivity <avi@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Zhang, Yanmin <yanmin_zhang@linux.intel.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
index da3d4e8..ee25ee9 100644
--- a/tools/perf/util/map.c
+++ b/tools/perf/util/map.c
@@ -629,14 +629,14 @@
 	}
 }
 
-char *machine__mmap_name(struct machine *self, char *buff)
+char *machine__mmap_name(struct machine *self, char *bf, size_t size)
 {
 	if (machine__is_host(self))
-		sprintf(buff, "[%s]", "kernel.kallsyms");
+		snprintf(bf, size, "[%s]", "kernel.kallsyms");
 	else if (machine__is_default_guest(self))
-		sprintf(buff, "[%s]", "guest.kernel.kallsyms");
+		snprintf(bf, size, "[%s]", "guest.kernel.kallsyms");
 	else
-		sprintf(buff, "[%s.%d]", "guest.kernel.kallsyms", self->pid);
+		snprintf(bf, size, "[%s.%d]", "guest.kernel.kallsyms", self->pid);
 
-	return buff;
+	return bf;
 }