xdg-desktop-portal-wlr: Segfault when using greetd + Sway

I’m using greetd as login manager with the GTK greeter and Sway.
This setup is more or less explained here and here.

After a specific upgrade, the greeter now takes a few seconds to start due to xdpw crashing and being restarted several times.

Here’s the log with -l DEBUG: xdpw.log

This is what coredumpctl info says:

[I] ~ $ coredumpctl info
           PID: 3072 (xdg-desktop-por)
           UID: 976 (greeter)
           GID: 976 (greeter)
        Signal: 11 (SEGV)
     Timestamp: Sun 2021-06-13 22:02:18 -03 (14min ago)
  Command Line: /usr/lib/xdg-desktop-portal-wlr -l DEBUG
    Executable: /usr/lib/xdg-desktop-portal-wlr
 Control Group: /user.slice/user-976.slice/user@976.service/app.slice/xdg-desktop-portal-wlr.service
          Unit: user@976.service
     User Unit: xdg-desktop-portal-wlr.service
         Slice: user-976.slice
     Owner UID: 976 (greeter)
       Boot ID: a52b1ef6df664d259ee863b9aa403656
    Machine ID: 3d14cd859eed44e78935812dd176271f
      Hostname: ryzen
       Storage: /var/lib/systemd/coredump/core.xdg-desktop-por.976.a52b1ef6df664d259ee863b9aa403656.3072.1623632538000000.zst (inaccessible)
       Message: Process 3072 (xdg-desktop-por) of user 976 dumped core.

                Stack trace of thread 3072:
                #0  0x00007fe571794515 __strlen_avx2 (libc.so.6 + 0x160515)
                #1  0x000055b5f806a5c2 n/a (xdg-desktop-portal-wlr + 0x45c2)
                #2  0x00007fe57165bb25 __libc_start_main (libc.so.6 + 0x27b25)
                #3  0x000055b5f806b05e n/a (xdg-desktop-portal-wlr + 0x505e)

About this issue

Original URL
State: closed
Created 3 years ago
Comments: 20 (1 by maintainers)

Commits related to this issue

config: handle missing HOME env variable gracefully Fixes: https://github.com/emersion/xdg-desktop-portal-wlr/issues/149 — committed to columbarius/xdg-desktop-portal-wlr by columbarius 3 years ago
config: handle missing HOME env variable gracefully Fixes: https://github.com/emersion/xdg-desktop-portal-wlr/issues/149 — committed to emersion/xdg-desktop-portal-wlr by columbarius 3 years ago

Most upvoted comments

If you build xdg-desktop-portal-wlr-git from AUR, it’ll include debugging symbols and you can send us a backtrace if you’re getting a segfault style crash in xdpw.

#0  0x00007feca2906515 in __strlen_avx2 () from /usr/lib/libc.so.6
#1  0x0000561452cf95ca in get_config_path () at ../xdg-desktop-portal-wlr-git/src/core/config.c:109
#2  init_config (config=0x7ffe4fc04eb0, configfile=<synthetic pointer>) at ../xdg-desktop-portal-wlr-git/src/core/config.c:165
#3  main (argc=1, argv=<optimized out>) at ../xdg-desktop-portal-wlr-git/src/core/main.c:84

I took a look at the code and it seems you are calling strlen over a NULL pointer, here:

	const char *home = getenv("HOME");
	size_t size_fallback = 1 + strlen(home) + strlen("/.config");

The environment variable HOME is not defined because greetd and greetd-gtkgreet run as the greeter user.
The greeter user has no home:

[I] ~ $ cat /etc/passwd|grep greeter
greeter:x:976:976:greetd greeter user:/:/bin/bash

Now that I think of, isn’t HOME guaranteed to be always defined?

Let me know if you need anything else.

itaranto on Jun 17, 2021

@itaranto Thanks for finding hat. Never came to my mind, that xdpw could run as a system user without home.

That’s strange, I’ll probably do more research, for example xdg-desktop-portal has HOME defined in my regular session but not in the greetd session.

Could you test if #151 fixes it, please?

Yes, I just built xdg-desktop-portal-wlr-git and it didn’t crashed in the greetd’s login screen.

itaranto on Jun 17, 2021

@itaranto Thanks for finding hat. Never came to my mind, that xdpw could run as a system user without home.

Could you test if #151 fixes it, please?

columbarius on Jun 17, 2021

You nailed it! This is a regression. @columbarius, can we make these getenv calls safe? If you don’t have time, I may be able to push a PR tomorrow evening.

getenv calls are “safe” by default in that they either return a string or NULL, we just need to check for that.

columbarius on Jun 17, 2021

You nailed it! This is a regression. @columbarius, can we make these getenv calls safe? If you don’t have time, I may be able to push a PR tomorrow evening.

danshick on Jun 17, 2021

Ugh, that shoots that theory. Any change in the logs?

It’s strange, xdpw is still crashing but now there’s no logs.

Another strange thing is that I found a crash for gtkgreet that I can reproduce 100% of the time. Every time I enter an incorrect password it segfaults, with a correct one it doesn’t. I’ll report that to greetd-gtkgreet.
I think this is probably unrelated to xdwp.

itaranto on Jun 16, 2021