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    SubjectRe: [resend][PATCH] Added PR_SET_PROCTITLE_AREA option for prctl()
    On Fri, Oct 9, 2009 at 10:42 PM, Andrew Morton
    <> wrote:

    >> >> + __ __ __ __ __ __ __ __ __ __ __ __ __ __ res += access_process_vm(task, mm->env_start,
    > Your email client is converting tabs to non-ascii crap.  gmail.  Sigh.

    Weird ... I'll have to see if I can do something about that :/

    > OK.
    > But there's no way in which the reader of either the patch or the
    > resulting code can discover this subtlety.

    I didn't write the log message or the code - I just mentioned these
    same issues back in the lkml thread :) But yes, this should be
    mentioned somewhere.

    >> The solution is to use the seqlock to detect this, and prevent the
    >> secret information from ever making it back to process B's userspace.
    >> Note that it's not enough to just recheck arg_start, as process A may
    >> reassign the proctitle area back to its original position after having
    >> it somewhere else for a while.
    > Well seqlock is _a_ solution.  Another is to use a mutex or an rwsem
    > around the whole operation.
    > With the code as you propose it, what happens if a process sits in a
    > tight loop running setproctitle?  Do other processes running `ps' get
    > stuck in a livelock until the offending process gets scheduled out?

    It does seem like a maximum spin count should be put in there - and
    maybe a timeout as well (since with FUSE etc it's possible to engineer
    page faults that take arbitrarily long).
    Also, it occurs to me that:

    > + do {
    > + seq = read_seqbegin(&mm->arg_lock);
    > +
    > + len = mm->arg_end - mm->arg_start;
    > + if (len > PAGE_SIZE)
    > + len = PAGE_SIZE;

    If arg_end or arg_start are modified after this, is it truly safe to
    assume that len will remain <= PAGE_SIZE without a memory barrier
    before the conditional?
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      Last update: 2009-10-10 05:03    [W:0.022 / U:38.824 seconds]
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