[PATCH 1/1] ip: ip_print: if no json obj is initialized default fp is stdout

[Julien Fortin]

From: Julien Fortin <jul...@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
    #3  0x000000000040ccd2 in print_int (value=<optimized out>, fmt=0x45460d 
“%d: “, key=0x4545fc “ifindex”, t=PRINT_ANY) at ip_common.h:189
    #4  print_linkinfo (who=<optimized out>, n=0x7fffffffa380, 
arg=0x7ffff77a82a0 <_IO_2_1_stdout_>) at ipaddress.c:1107
    #5  0x0000000000422e13 in accept_msg (who=0x7fffffff8320, 
ctrl=0x7fffffff8310, n=0x7fffffffa380, arg=0x7ffff77a82a0 <_IO_2_1_stdout_>) at 
ipmonitor.c:89
    #6  0x000000000044c58f in rtnl_listen (rtnl=0x672160 <rth>, 
handler=handler@entry=0x422c70 <accept_msg>, jarg=0x7ffff77a82a0 
<_IO_2_1_stdout_>)
        at libnetlink.c:761
        #7  0x00000000004233db in do_ipmonitor (argc=<optimized out>, 
argv=0x7fffffffe5a0) at ipmonitor.c:310
        #8  0x0000000000408f74 in do_cmd (argv0=0x7fffffffe7f5 “mon”, argc=3, 
argv=0x7fffffffe588) at ip.c:116
        #9  0x0000000000408a94 in main (argc=4, argv=0x7fffffffe580) at ip.c:311

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 <d...@cumulusnetworks.com>
Reviewed-by: David Ahern <d...@cumulusnetworks.com>
Signed-off-by: Julien Fortin <jul...@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..8cce2011 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