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    SubjectRe: [PATCH] Make /proc/slabinfo 0400
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    On Fri, 2011-03-04 at 09:48 -0800, Linus Torvalds wrote:
    > 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).

    I think lying to the user is much worse than changing the permissions.
    The cost of the resulting confusion is WAY higher.

    --
    Mathematics is the supreme nostalgia of our time.




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