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    SubjectRe: [PATCH v3] sysctl: control functionality of /proc/pid/mem
    On Mon, 23 Jan 2012 13:21:15 -0800
    Kees Cook <keescook@chromium.org> wrote:

    >
    > Add the "proc_pid_mem" sysctl to control whether or not /proc/pid/mem is
    > allowed to work: 0: disabled, 1: read only, 2: read/write (default).
    >
    > Signed-off-by: Kees Cook <keescook@chromium.org>
    > ---
    > v3:
    > - document the default, thanks to Randy Dunlap.
    > - remove needless CONFIG_PROC_FS checks, thanks to Eric W. Biederman.

    I was wondering about that. Is CONFIG_PROC_FS=n, CONFIG_SYSCTL=y an
    impossible combination? If so, why?

    > --- a/Documentation/sysctl/kernel.txt
    > +++ b/Documentation/sysctl/kernel.txt
    > @@ -56,6 +56,7 @@ show up in /proc/sys/kernel:
    > - printk_delay
    > - printk_ratelimit
    > - printk_ratelimit_burst
    > +- proc_pid_mem
    > - randomize_va_space
    > - real-root-dev ==> Documentation/initrd.txt
    > - reboot-cmd [ SPARC only ]
    > @@ -477,6 +478,20 @@ send before ratelimiting kicks in.
    >
    > ==============================================================
    >
    > +proc_pid_mem:
    > +
    > +This option can be used to select the level of access given to potential
    > +ptracers when using the per-process "mem" file in /proc/pid/mem.
    > +
    > +0 - Disable entirely.
    > +
    > +1 - Allow potential ptracers read access to process memory, but not writes.
    > +
    > +2 - Allow potential ptracers read and write access to process memory. This
    > + is the default.
    > +
    > +==============================================================

    I agree with Colin on this (he stole my line!).



    Overall, the patch looks really hacky and random. I felt the same way
    as Vasily: it's easy to see how a significant number of similar (and
    hacky and random) patches could be added, resulting in a regrettable
    mess.

    Is there some better designed, more organized way of approaching all of
    this? Random ideas:

    - A parallel /procfs-perms filesystem. You write a number into
    /procfs-perms/stat to affect access to /proc/stat (although why the
    heck not just run `chmod /proc/stat'?) It's unclear how to handle
    /proc/pid/. Perhaps literally have a /procfs-perms/pid/ directory.

    - Make tasks inherit their /proc/pid/* permissions across fork, do a
    chmod /proc/1/whatever in initscripts.

    - Other and better things ;) This particular approach makes my toes
    curl.





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