[PATCH iproute2 v2] ip: ip_print: if no json obj is initialized default fp is stdout

[Julien Fortin <julien@cumulusnetworks.com>]

From: Julien Fortin <julien@cumulusnetworks.com>

The ip monitor didn't call `new_json_obj` (even for in non json context),
so the static FILE* _fp variable wasn't initialized, thus raising a
SIGSEGV in ipaddress.c. This patch should fix this issue for good, new
paths won't have to call `new_json_obj`.

$ ip -t mon label link
fmt=fmt@entry=0x45460d “%d: “, value=<optimized out>) at ip_print.c:132
at libnetlink.c:761

Traceback can be seen when running the following command in a new terminal.
$ ip link add dev br0 type bridge

Fixes: 6377572f ("ip: ip_print: add new API to print JSON or regular format output")
Reported-by: David Ahern <dsa@cumulusnetworks.com>
Reviewed-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>
---
 ip/ip_print.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/ip/ip_print.c b/ip/ip_print.c
index 4cd6a0bc..7eb4c6da 100644
--- a/ip/ip_print.c
+++ b/ip/ip_print.c
@@ -23,6 +23,11 @@ static FILE *_fp;
 #define _IS_JSON_CONTEXT(type) ((type & PRINT_JSON || type & PRINT_ANY) && _jw)
 #define _IS_FP_CONTEXT(type) (!_jw && (type & PRINT_FP || type & PRINT_ANY))
 
+static inline FILE *_get_fp(void)
+{
+	return _fp ? _fp : stdout;
+};
+
 void new_json_obj(int json, FILE *fp)
 {
 	if (json) {
@@ -91,7 +96,7 @@ void open_json_array(enum output_type type, const char *str)
 			jsonw_name(_jw, str);
 		jsonw_start_array(_jw);
 	} else if (_IS_FP_CONTEXT(type)) {
-		fprintf(_fp, "%s", str);
+		fprintf(_get_fp(), "%s", str);
 	}
 }
 
@@ -105,7 +110,7 @@ void close_json_array(enum output_type type, const char *str)
 		jsonw_end_array(_jw);
 		jsonw_pretty(_jw, true);
 	} else if (_IS_FP_CONTEXT(type)) {
-		fprintf(_fp, "%s", str);
+		fprintf(_get_fp(), "%s", str);
 	}
 }
 
@@ -126,7 +131,7 @@ void close_json_array(enum output_type type, const char *str)
 			else						\
 				jsonw_##type_name##_field(_jw, key, value); \
 		} else if (_IS_FP_CONTEXT(t)) {				\
-			color_fprintf(_fp, color, fmt, value);          \
+			color_fprintf(_get_fp(), color, fmt, value);	\
 		}							\
 	}
 _PRINT_FUNC(int, int);
@@ -149,7 +154,7 @@ void print_color_string(enum output_type type,
 		else
 			jsonw_string_field(_jw, key, value);
 	} else if (_IS_FP_CONTEXT(type)) {
-		color_fprintf(_fp, color, fmt, value);
+		color_fprintf(_get_fp(), color, fmt, value);
 	}
 }
 
@@ -170,7 +175,7 @@ void print_color_bool(enum output_type type,
 		else
 			jsonw_bool(_jw, value);
 	} else if (_IS_FP_CONTEXT(type)) {
-		color_fprintf(_fp, color, fmt, value ? "true" : "false");
+		color_fprintf(_get_fp(), color, fmt, value ? "true" : "false");
 	}
 }
 
@@ -189,7 +194,7 @@ void print_color_0xhex(enum output_type type,
 		snprintf(b1, sizeof(b1), "%#x", hex);
 		print_string(PRINT_JSON, key, NULL, b1);
 	} else if (_IS_FP_CONTEXT(type)) {
-		color_fprintf(_fp, color, fmt, hex);
+		color_fprintf(_get_fp(), color, fmt, hex);
 	}
 }
 
@@ -208,7 +213,7 @@ void print_color_hex(enum output_type type,
 		else
 			jsonw_string(_jw, b1);
 	} else if (_IS_FP_CONTEXT(type)) {
-		color_fprintf(_fp, color, fmt, hex);
+		color_fprintf(_get_fp(), color, fmt, hex);
 	}
 }
 
@@ -228,6 +233,6 @@ void print_color_null(enum output_type type,
 		else
 			jsonw_null(_jw);
 	} else if (_IS_FP_CONTEXT(type)) {
-		color_fprintf(_fp, color, fmt, value);
+		color_fprintf(_get_fp(), color, fmt, value);
 	}
 }
-- 
2.14.1