[PATCH] perf data convert: Output empty string for null pointer

[kotborealis]

From: Evgeny Pistun <kotborealis@xxxxxxxx>

Providing ill-formed input to `perf data conver --to-json`
causes it to crash with segmentaton fault. There's a bug in
`output_json_string` functon: input string is not validated.
This could be reproduced by crafting input that does not specify
hostname/os-release/etc, which are written to 'headers' section of
outputted json.

This patch adds a null pointer check. If `output_json_string` is
called with a null pointer, it should output empty string (`""`).

Signed-off-by: Evgeny Pistun <kotborealis@xxxxxxxx>
---
 tools/perf/util/data-convert-json.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/data-convert-json.c b/tools/perf/util/data-convert-json.c
index 5bb3c2ba9..f8fd22bd7 100644
--- a/tools/perf/util/data-convert-json.c
+++ b/tools/perf/util/data-convert-json.c
@@ -42,7 +42,7 @@ struct convert_json {
 static void output_json_string(FILE *out, const char *s)
 {
 	fputc('"', out);
-	while (*s) {
+	while (s != NULL && *s) {
 		switch (*s) {
 
 		// required escapes with special forms as per RFC 8259
-- 
2.25.1