perf record: Prevent reading invalid data in record__mmap_read

When record__mmap_read() requires data more than the size of ring
buffer, drop those data to avoid accessing invalid memory.

This can happen when reading from overwritable ring buffer, which
should be avoided. However, check this for robustness.
Signed-off-by: NWang Nan <wangnan0@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1463987628-163563-3-git-send-email-wangnan0@huawei.comSigned-off-by: NHe Kuang <hekuang@huawei.com>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-record.c

@@ -40,6 +40,7 @@
 #include <unistd.h>
 #include <sched.h>
 #include <sys/mman.h>
+#include <asm/bug.h>
 
 
 struct record {
@@ -98,6 +99,13 @@ static int record__mmap_read(struct record *rec, int idx)
 	rec->samples++;
 
 	size = head - old;
+	if (size > (unsigned long)(md->mask) + 1) {
+		WARN_ONCE(1, "failed to keep up with mmap data. (warn only once)\n");
+
+		md->prev = head;
+		perf_evlist__mmap_consume(rec->evlist, idx);
+		return 0;
+	}
 
 	if ((old & md->mask) + size != (head & md->mask)) {
 		buf = &data[old & md->mask];