netdev - Re: KASAN: stack-out-of-bounds Read in xfrm_state

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Date:   Fri, 2 Feb 2018 09:23:30 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Steffen Klassert <steffen.klassert@...unet.com>
Cc:     syzbot <syzbot+e1a1577ca8bcb47b769a@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: stack-out-of-bounds Read in xfrm_state_find (4)

On Fri, Feb 2, 2018 at 8:22 AM, Steffen Klassert
<steffen.klassert@...unet.com> wrote:
> On Thu, Feb 01, 2018 at 11:30:00AM +0100, Dmitry Vyukov wrote:
>> On Thu, Feb 1, 2018 at 9:34 AM, Steffen Klassert
>>
>> Hi Steffen,
>>
>> Please see the email footer:
>>
>> > If you want to test a patch for this bug, please reply with:
>> > #syz test: git://repo/address.git branch
>> > and provide the patch inline or as an attachment.
>
> Thanks for the hint, I've overlooked this. This is very usefull
> for the case that I can not reproduce the bug, but I think I know
> how to fix it.
>
> There are two more cases that come to my mind where syzbot could
> help.
>
> 1. I can not reproduce the bug and I don't know how to fix it,
>    but some debug output would be helpfull:
>
>    syz test-debug-patch-and-send-dmesg-output: git://repo/address.git branch

This is supported by "syz test", see:
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#communication-with-syzbot


> 2. I can not reproduce the bug and I have absolutely no idea what it
>    could be:
>
>    syz bisect: git://repo/address.git branch commit a commit b
>
> I don't know if this is possible, but it would bring the bugfixing
> process a bit coser to the case where a real user does a bug report.

This is on my plate:
https://github.com/google/syzkaller/issues/501
I think we probably will do bisection always without user request, and
then just post an additional email with results.


> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>
>
> Subject: [PATCH RFC] xfrm: Refuse to insert 32 bit userspace socket policies on 64 bit systems
>
> We don't have compat layer for xfrm, so userspace and kernel
> structures have different sizes in this case. This results in
> a broken confuguration, so refuse to configure socket policies
> when trying to insert from 32 bit userspace as we do it already
> with policies inserted via netlink.
>
> Reported-by: syzbot+e1a1577ca8bcb47b769a@...kaller.appspotmail.com
> Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
> ---
>  net/xfrm/xfrm_state.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
> index a3785f538018..25861a4ef872 100644
> --- a/net/xfrm/xfrm_state.c
> +++ b/net/xfrm/xfrm_state.c
> @@ -2056,6 +2056,11 @@ int xfrm_user_policy(struct sock *sk, int optname, u8 __user *optval, int optlen
>         struct xfrm_mgr *km;
>         struct xfrm_policy *pol = NULL;
>
> +#ifdef CONFIG_COMPAT
> +       if (in_compat_syscall())
> +               return -EOPNOTSUPP;
> +#endif
> +
>         if (optlen <= 0 || optlen > PAGE_SIZE)
>                 return -EMSGSIZE;
>
> --
> 2.14.1
>