/usr/bin/w -s segfaults

[Marius Vollmer]

procps 2:4.0.4-4ubuntu3

Just running "w -s" segfaults:

# w -s
 07:55:26 up 8 min, 3 users, load average: 0.00, 0.03, 0.02
USER TTY FROM IDLE WHAT
Segmentation fault (core dumped)

I see if I can get a backtrace.

[Marius Vollmer (marius-vollmer-gmail)]

Program received signal SIGSEGV, Segmentation fault.
print_host (
    host=host@entry=0x4c <error: Cannot access memory at address 0x4c>,
    len=16, len@entry=256, fromlen=fromlen@entry=16) at src/w.c:112
112 if (*host == '\0') break;
(gdb) bt
#0 print_host (
    host=host@entry=0x4c <error: Cannot access memory at address 0x4c>,
    len=16, len@entry=256, fromlen=fromlen@entry=16) at src/w.c:112
#1 0x0000555555557161 in print_from (session=session@entry=0x0,
    u=u@entry=0x0, ip_addresses=ip_addresses@entry=0, fromlen=fromlen@entry=16)
    at src/w.c:264
#2 0x00005555555580e0 in showinfo (session=0x555555560580 "3",
    name=name@entry=0x555555560770 "root", u=u@entry=0x0,
    formtype=formtype@entry=0, maxcmd=maxcmd@entry=35, from=from@entry=1,
    userlen=8, fromlen=16, ip_addresses=0, pids=0) at src/w.c:622
#3 0x0000555555556a8f in main (argc=<optimized out>, argv=<optimized out>)
    at src/w.c:831

[Marius Vollmer (marius-vollmer-gmail)]

Ah, it's an old bug: https://gitlab.com/procps-ng/procps/-/issues/301

[Sebastien Bacher (seb128)]

The issue got fixed upstream in https://gitlab.com/procps-ng/procps/-/commit/79042e07 but it isn't in the current Debian/Ubuntu version yet

[Alex Murray (alexmurray)]

I think a follow-up commit might also be needed https://gitlab.com/procps-ng/procps/-/commit/b113806ccfa706e73bc2e0005eb7606d08c03850 since the code to print the results from sd_get_sessions() still has the wrong test of `if (sessions >= 0)` - this instead should be `if (sessions > 0)` which is corrected in this additional commit