Re: [PATCH v2] twist: allow converting pr_devel()/pr_debug() into snprintf()

[Petr Mladek <pmladek@suse.com>]

On Thu 2020-05-28 15:56:03, Tetsuo Handa wrote:
> syzbot found a NULL pointer dereference bug inside mptcp_recvmsg() due to
> ssock == NULL, but this bug manifested inside selinux_socket_recvmsg()
> because pr_debug() was no-op [1].
> 
>   pr_debug("fallback-read subflow=%p",
>            mptcp_subflow_ctx(ssock->sk));
>   copied = sock_recvmsg(ssock, msg, flags);
> 
> Thus, let's allow fuzzers to always evaluate pr_devel()/pr_debug()
> messages, by redirecting no-op pr_devel()/pr_debug() calls to snprintf().
> 
> [1] https://syzkaller.appspot.com/bug?id=12be9aa373be9d8727cdd172f190de39528a413a
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Petr Mladek <pmladek@suse.com>
> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ondrej Mosnacek <omosnace@redhat.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> ---
>  include/linux/dev_printk.h    | 16 ++++++++++++++++
>  include/linux/dynamic_debug.h | 14 ++++++++++++--
>  include/linux/printk.h        | 10 ++++++++++
>  lib/Kconfig.twist             | 12 ++++++++++++
>  4 files changed, 50 insertions(+), 2 deletions(-)

I am fine with pushing this into linux-next for testing purposes.
But I am against pushing this to Linus' tree in this form.

Now, it requires lib/Kconfig.twist that is added by a patch in
Andrew's tree. One approach is to push this into linux-next
via Andrew's -mm tree.

Another possibility would be to remove lib/Kconfig.twist
changes from this patch and replace
CONFIG_TWIST_ALWAYS_EVALUATE_PRINTK_ARGUMENTS with
CONFIG_TWIST_FOR_SYZKALLER_TESTING.
Then I could push it into linux-next via printk/linux.git tree.

Best Regards,
Petr