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

On Wed, 20 Sep 2017 15:19:14 -0700
Julien Fortin [off-list ref] wrote:

From: Julien Fortin <redacted>

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 <redacted>
Reviewed-by: David Ahern <redacted>
Signed-off-by: Julien Fortin <redacted>
---

The fix looks correct, but the patch has minor style format issue.

ERROR: "foo* bar" should be "foo *bar"
#54: FILE: ip/ip_print.c:26:
+static inline FILE* _get_fp(void)