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    SubjectRe: [PATCH] Make /proc/slabinfo 0400
    On Fri, Mar 4, 2011 at 9:36 AM, Dave Hansen <dave@linux.vnet.ibm.com> wrote:
    >
    > We need to either keep the bad guys away from the counts (this patch),
    > or de-correlate the counts moving around with the position of objects in
    > the slab.  Ted's suggestion is a good one, and the only other thing I
    > can think of is to make the values useless, perhaps by batching and
    > delaying the (exposed) counts by a random amount.

    We might just decide to expose the 'active' count for regular users
    (and then, in case there are tools there that parse this as normal
    users, we could set the 'total' fields to be the same as the active
    one, possibly rounded up to the slab allocation or something.

    I know, I know, from a memory usage standpoint, 'active' is secondary,
    but it still correlates fairly well, so it's still useful. And for
    seeing memory leaks (as opposed to slab fragmentation etc issues),
    it's actually the interesting case.

    And at the same time, it's actually much less involved with actual
    physical allocations than 'total' is, and thus much less of an attack
    vector. The fact that we got another socket allocation when we opened
    a new socket is not "useful" information for an attacker, not in the
    way it is to see a hint of _where_ the socket got allocated.

    Of course, as you say, '/proc/meminfo' still does give you the trigger
    for "oh, now somebody actually allocated a new page". That's totally
    independent of slabinfo, though (and knowing the number of active
    slabs would neither help nor hurt somebody who uses meminfo - you
    might as well allocate new sockets in a loop, and use _only_ meminfo
    to see when that allocated a new page).

    Linus
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