Instead of changing the working directory before launching the incubator process,
this now just changes the working directory after dropping privileges, at which
point we're more likely to be able to enter the user's home directory since we're
running as the user.
For paths that use the 'login' or 'su -l' commands, those already take care of changing
the working directory to the user's home directory.
Fixes#13120
Signed-off-by: Percy Wegmann <percy@tailscale.com>
This involved the following:
1. Pass the su command path as first of args in call to unix.Exec to make sure that busybox sees the correct program name.
Busybox is a single executable userspace that implements various core userspace commands in a single binary. You'll
see it used via symlinking, so that for example /bin/su symlinks to /bin/busybox. Busybox knows that you're trying
to execute /bin/su because argv[0] is '/bin/su'. When we called unix.Exec, we weren't including the program name for
argv[0], which caused busybox to fail with 'applet not found', meaning that it didn't know which command it was
supposed to run.
2. Tell su to whitelist the SSH_AUTH_SOCK environment variable in order to support ssh agent forwarding.
3. Run integration tests on alpine, which uses busybox.
4. Increment CurrentCapabilityVersion to allow turning on SSH V2 behavior from control.
Fixes#12849
Signed-off-by: Percy Wegmann <percy@tailscale.com>
This allows the SSH_AUTH_SOCK environment variable to work inside of
su and agent forwarding to succeed.
Fixes#12467
Signed-off-by: Percy Wegmann <percy@tailscale.com>
This allows pam authentication to run for ssh sessions, triggering
automation like pam_mkhomedir.
Updates #11854
Signed-off-by: Percy Wegmann <percy@tailscale.com>
