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From:   Eric Dumazet <edumazet@google.com>
Date:   Mon, 30 Oct 2023 09:59:54 +0100
Message-ID: <CANn89iJyLWy6WEa_1p+jKpGBfq=h=TX=_7p_-_i4j6mHcMXbgA@mail.gmail.com>
Subject: Re: [PATCH net] dccp: check for ccid in ccid_hc_tx_send_packet
To:     Bragatheswaran Manickavel <bragathemanick0908@gmail.com>
Cc:     davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com,
        dccp@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        syzbot+c71bc336c5061153b502@syzkaller.appspotmail.com
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On Sat, Oct 28, 2023 at 4:41=E2=80=AFPM Bragatheswaran Manickavel
<bragathemanick0908@gmail.com> wrote:
>
> ccid_hc_tx_send_packet might be called with a NULL ccid pointer
> leading to a NULL pointer dereference
>
> Below mentioned commit has similarly changes
> commit 276bdb82dedb ("dccp: check ccid before dereferencing")
>
> Reported-by: syzbot+c71bc336c5061153b502@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=3Dc71bc336c5061153b502
> Signed-off-by: Bragatheswaran Manickavel <bragathemanick0908@gmail.com>
> ---
>  net/dccp/ccid.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/dccp/ccid.h b/net/dccp/ccid.h
> index 105f3734dadb..1015dc2b9392 100644
> --- a/net/dccp/ccid.h
> +++ b/net/dccp/ccid.h
> @@ -163,7 +163,7 @@ static inline int ccid_packet_dequeue_eval(const int =
return_code)
>  static inline int ccid_hc_tx_send_packet(struct ccid *ccid, struct sock =
*sk,
>                                          struct sk_buff *skb)
>  {
> -       if (ccid->ccid_ops->ccid_hc_tx_send_packet !=3D NULL)
> +       if (ccid !=3D NULL && ccid->ccid_ops->ccid_hc_tx_send_packet !=3D=
 NULL)
>                 return ccid->ccid_ops->ccid_hc_tx_send_packet(sk, skb);
>         return CCID_PACKET_SEND_AT_ONCE;
>  }
> --
> 2.34.1
>

If you are willing to fix dccp, I would make sure that some of
lockless accesses to dccps_hc_tx_ccid
are also double checked and fixed.

do_dccp_getsockopt() and dccp_get_info()