perf tools: Ensure sscanf does not overrun the "mem" field

Make the parsing robust.

(perf has some other assumptions that BUFSIZE <= MAX_PATH which are
not touched here)

Reported-by: Jackie Chang
Signed-off-by: Alan Cox <[e-mail]>
Cc: Alan Cox <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/n/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/header.c

···
 		/* skip over invalid lines */
 		if (!strchr(buf, ':'))
 			continue;
-		if (sscanf(buf, "%*s %*d %s %"PRIu64, field, &mem) != 2)
+		if (sscanf(buf, "%*s %*d %31s %"PRIu64, field, &mem) != 2)
 			goto done;
 		if (!strcmp(field, "MemTotal:"))
 			mem_total = mem;