What to do when a closed-source program don't honour $HOME to locate its files?

snapcraft
1

I’m attempting to fix the issue where ngrok need to save an authtoken in it’s config directory (~/.ngrok2/authtoken), and found out that it doesn’t honor the $HOME environment variable but (possibly) queried it via /etc/passwd (which is the real home directory, not the one in the snap runtime):

%E5%9C%96%E7%89%87
%E5%9C%96%E7%89%87999×705 73 KB

It’s less likely that we can change its own code to honor the HOME environment variable, is there any hacks that can workaround this?

2

The executable seems to be dynamically linked, though:

$ file ngrok
ngrok: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, Go BuildID=WurpW0l_bKdI4kv9WPWp/N2JKHdyhG6WVkZMzAaOv/82jPo5YLbjXZotiOUoun/1WB10Ln2gz9Y8HZSFsV-, not stripped

$ ldd ngrok
        linux-vdso.so.1 (0x00007ffe2ba79000)
        libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fc63c3ed000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fc63c202000)
        /lib64/ld-linux-x86-64.so.2 (0x00007fc63c434000)

Maybe some dynamic linker magic would help?

3

Hi there, have you tried using layouts? https://docs.snapcraft.io/snap-layouts

4

How would the layouts feature help with this situation?

5

Layouts are about exposing things from SNAP, SNAP_DATA and SNAP_COMMON to other parts of the filesystem. It isn’t explicitly listed in the documentation page you listed, but SNAP_USER_DATA and SNAP_USER_COMMON are not currently supported, which is needed for supporting /home.

1 Like
6

Likely. You can strace the application and see what it is doing (likely getpwent) and then craft an LD_PRELOAD.

1 Like