On Tue, Apr 10, 2018 at 5:35 PM, Stephan Mueller <smuel...@chronox.de> wrote:
> Am Dienstag, 10. April 2018, 17:23:46 CEST schrieb Dmitry Vyukov:
> Hi Dmitry,
>> Stephan,
>> Do you have any hypothesis as to why this is not detected by KASAN and
>> causes silent corruptions?
>> We generally try to understand such cases and improve KASAN so that it
>> catches such cases more reliably and they do not cause splashes of
>> random crashes on syzbot.
> I do not have any hypothesis at this point. I know that you induce some fault.
> As you mentioned the drbg_kcapi_seed function, I was looking through the error
> code paths to see whether some error handlers trip over each other. But all is
> guesswork so far. And I am not even sure whether the bug is in the DRBG code
> base.
> Looking into the trace you sent, I see a NULL pointer dereference. At one
> point there is also the drbg_init_hash_kernel that is called. But nowhere I
> see any smoking gun.
> Could you please give me a description of the fault you are inducing?

Hi Stephan,

What do you mean by description of the fault?
It's kernel standard FAULT_INJECTION facility, it injects faults
mainly into kmalloc/slab_alloc (also in a bunch of other things, but
in this case this seems to be kmalloc). In the repro you can see that
it's injecting a fault into 8-th malloc in the setsockopt syscall.

I wonder why you can't reproduce it. I can trigger it reliably in a
qemu. Let's try this:
I have upstream kernel on b284d4d5a6785f8cd07eda2646a95782373cd01e.
Here is my config:
Here is the compiler:
Build as: make -jN CC=that/gcc/bin/gcc
Then I start qemu as:

qemu-system-x86_64 -hda wheezy.img -net
user,host=,hostfwd=tcp::10022-:22 -net nic -nographic -kernel
arch/x86/boot/bzImage -append "kvm-intel.nested=1
kvm-intel.unrestricted_guest=1 kvm-intel.ept=1
kvm-intel.flexpriority=1 kvm-intel.vpid=1
kvm-intel.emulate_invalid_guest_state=1 kvm-intel.eptad=1
kvm-intel.enable_shadow_vmcs=1 kvm-intel.pml=1
kvm-intel.enable_apicv=1 console=ttyS0 root=/dev/sda
earlyprintk=serial slub_debug=UZ vsyscall=native rodata=n oops=panic
panic_on_warn=1 panic=86400" -enable-kvm -pidfile vm_pid -m 2G -smp 4
-cpu host

You can find the wheezy.img and ssh key for it here:

Then I compile this program:
as: gcc prog.c -static -m32

Run in the qemu and within a minute it gives me the crash.

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