On Thu, May 03, 2018 at 23:25:05 +0200, Michael Biebl wrote: > Well, logind is running as root, but the the service file is locked down > considerably: > > CapabilityBoundingSet=CAP_SYS_ADMIN CAP_MAC_ADMIN CAP_AUDIT_CONTROL > CAP_CHOWN CAP_KILL CAP_DAC_REA > MemoryDenyWriteExecute=yes > RestrictRealtime=yes > RestrictNamespaces=yes > RestrictAddressFamilies=AF_UNIX AF_NETLINK AF_INET AF_INET6 > SystemCallFilter=~@clock @cpu-emulation @debug @keyring @module > @obsolete @raw-io @reboot @swap > SystemCallArchitectures=native > LockPersonality=yes > IPAddressDeny=any > FileDescriptorStoreMax=512 > > You will probably have to tweak those settings yourself, if you want to > continue to use hidepid
Looking at the Linux code, neither uid 0 or gid 0 is actually special-
cased [fs/proc/base.c]:
static bool has_pid_permissions(struct pid_namespace *pid,
struct task_struct *task,
int hide_pid_min)
{
if (pid->hide_pid < hide_pid_min)
return true;
if (in_group_p(pid->pid_gid))
return true;
return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
}
So I guess it's always just looked like root had special access (e.g.,
"ps aux" works fine as uid=gid=0 with no supplementary groups), based on
that ptrace permission which logind probably lacks.
I found the file you're quoting from in /lib/systemd/system/. What's
the recommended way to do local changes? Copy to /etc/systemd/system/
and edit?
This failure is really obscure. Perhaps logind should try to open
/proc/1 when it hits this case, and log an explicit message about
hidepid if it gets ENOENT there.
-- Michael
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