Hi Linus,

On Mon, Sep 19, 2011 at 9:55 PM, Linus Torvalds
[off-list ref] wrote:

Also, quite frankly, your argument that /proc/slabinfo is so important
for kernel debugging is bogus. Every time I've complained about the
fact that the thing is useless AND ACTIVELY MISLEADING because it
mixes up all the slabs (so big numbers for "vm_area_struct" might
actually be about some other slab entirely, and *has* been, to the
point of people wasting time), the answer has been "whatever".

You can't have it both ways just to argue for the status quo.

Well, sure. I was actually planning to rip out SLUB merging completely
because it makes /proc/slabinfo so useless but never got around doing
that. Mixing up allocations makes heap exploits harder but there's no
agreement on how much more difficult (i.e. if it matters at all for brute
force attacks).

So dunno what's the right thing to do here. Every time I discuss the
issues with 'security folks' I'm left with more questions than answers...
Everybody seems to be more interested in closing down kernel ABIs
rather than making kernel memory allocations more robust against
attacks.

But anyway, if you feel about this strongly feel free to pick up
Vasiliy's patch. I think my suggestion of introducing a
CONFIG_RESTRICT_PROCFS makes most sense because:

  - When we've mucked around with /proc/slabinfo in the past, we have
    broken setups. (That might be less relevant now.)

  - /proc/slabinfo is not the only source where you can get information
    on kernel memory allocations (we have one in sysfs and perf kmem).

On Mon, Sep 19, 2011 at 9:55 PM, Linus Torvalds
[off-list ref] wrote:

Considering how useless /proc/slabinfo actually is today - exactly
because of the misleading mixing - I suspect the right thing to do is
to make it root-only.

Having some aggregate number in /proc/meminfo would probably be fine.

And yes, we probably should avoid giving page-level granularity in
/proc/meminfo too. Do it in megabytes instead. None of the information
there is really relevant at a page level, everybody just wants rough
aggregates.

We have this in /proc/meminfo:

Slab:              20012 kB

Or did you mean something even more specific?

                        Pekka

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