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    SubjectRe: [PATCH][0/6] Change proc file permissions with sysctls
    On Sun, 20 Mar 2005, Rene Scharfe wrote:

    > The permissions of files in /proc/1 (usually belonging to init) are
    > kept as they are. The idea is to let system processes be freely
    > visible by anyone, just as before. Especially interesting in this
    > regard would be instances of login.

    I think you mean login shells, the login process is just the thing asking
    for the password agter the (m)ingetty got the username. These processes
    are usurally created with the '-' sign in argv[0][0], but the users may
    replace that string at will. I think it's still OK to depend on that if
    you want a semi-secure system.

    > I don't know how to easily
    > discriminate between system processes and "normal" processes inside
    > the kernel (apart from pid

    Do you mean ppid?

    > == 1 and uid == 0 (which is too broad)).
    > Any ideas?

    This feature seems to be frequently requested. I don't remember the
    outcome, though.

    From a quick view, it seems the symlinks in /proc are empty for kernel
    threads and non-empty for user processes. Since you're messing with the
    proc entries, this could be a cheap way to find the kernel threads.
    Another possibility is by looking at the blocked signals, signal 9 may not
    be blocked by mortals.

    For the system daemons, you could additionally check for the absence of a
    controlling tty, but that's still no safe distinction from a process run
    by nohup. Checking for sid=pid will filter additional processes, but it
    the shell in midnight commander and screen are still false positives.
    Checking for */sbin*/ in $PID/command will fail as soon as the daemon
    overwrites argv[0].

    I don't think there is a relaible way to tell the system service daemons
    from screen except for the name, and you'll want to detect screen-alike
    programs, too.

    Top 100 things you don't want the sysadmin to say:
    40. The sprinkler system isn't supposed to leak is it?

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