[patch] perf report segfault with 0-sized strings

[Vince Weaver]

Hello,

the perf_data_fuzzer found an issue when strings have size 0.
malloc() in do_read_string() is happy to allocate a string of 
size 0 but when code (in this case the pmu parser) tries to work with 
those it will segfault.

Signed-off-by: Vince Weaver <vincent.weaver@xxxxxxxxx>

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index c24db7f4909c..641129efa987 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -251,6 +252,9 @@ static char *do_read_string(struct feat_fd *ff)
 	if (do_read_u32(ff, &len))
 		return NULL;
 
+	if (len==0)
+		return NULL;
+
 	buf = malloc(len);
 	if (!buf)
 		return NULL;
@@ -1781,6 +1785,10 @@ static void print_pmu_mappings(struct feat_fd *ff, FILE *fp)
 	str = ff->ph->env.pmu_mappings;
 
 	while (pmu_num) {
+
+		if (str==NULL)
+			goto error;
+
 		type = strtoul(str, &tmp, 0);
 		if (*tmp != ':')
 			goto error;