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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Tue, 31 Jul 2018 18:03:16 +0200
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Subject: Re: [PATCH v4 13/17] khwasan: add hooks implementation
To:     Christopher Lameter <cl@linux.com>
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On Tue, Jul 31, 2018 at 5:38 PM, Christopher Lameter <cl@linux.com> wrote:
> On Tue, 31 Jul 2018, Dmitry Vyukov wrote:
>
>> > Actually you should do this for SLAB_TYPESAFE_BY_RCU slabs. Usually they are with ->ctors but there
>> > are few without constructors.
>> > We can't reinitialize or even retag them. The latter will definitely cause false-positive use-after-free reports.
>>
>> Somewhat offtopic, but I can't understand how SLAB_TYPESAFE_BY_RCU
>> slabs can be useful without ctors or at least memset(0). Objects in
>> such slabs need to be type-stable, but I can't understand how it's
>> possible to establish type stability without a ctor... Are these bugs?
>> Or I am missing something subtle? What would be a canonical usage of
>> SLAB_TYPESAFE_BY_RCU slab without a ctor?
>
> True that sounds fishy. Would someone post a list of SLAB_TYPESAFE_BY_RCU
> slabs without ctors?

https://elixir.bootlin.com/linux/latest/source/fs/jbd2/journal.c#L2395
https://elixir.bootlin.com/linux/latest/source/fs/kernfs/mount.c#L415
https://elixir.bootlin.com/linux/latest/source/net/netfilter/nf_conntrack_core.c#L2065
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/i915/i915_gem.c#L5501
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/i915/selftests/mock_gem_device.c#L212
https://elixir.bootlin.com/linux/latest/source/drivers/staging/lustre/lustre/ldlm/ldlm_lockd.c#L1131

Also these in proto structs:
https://elixir.bootlin.com/linux/latest/source/net/dccp/ipv4.c#L959
https://elixir.bootlin.com/linux/latest/source/net/dccp/ipv6.c#L1048
https://elixir.bootlin.com/linux/latest/source/net/ipv4/tcp_ipv4.c#L2461
https://elixir.bootlin.com/linux/latest/source/net/ipv6/tcp_ipv6.c#L1980
https://elixir.bootlin.com/linux/latest/source/net/llc/af_llc.c#L145
https://elixir.bootlin.com/linux/latest/source/net/smc/af_smc.c#L105

They later created in net/core/sock.c without ctor.