linux-kernel - Re: [PATCH net] dccp: check for ccid in ccid_hc_tx_send

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Message-ID: <CANn89iKPTdE+oAB30gp4koC7ddnga20R8H6V3qismvvEP80aqg@mail.gmail.com>
Date:   Mon, 30 Oct 2023 16:49:06 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Bragatheswaran Manickavel <bragathemanick0908@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        dccp@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+c71bc336c5061153b502@...kaller.appspotmail.com
Subject: Re: [PATCH net] dccp: check for ccid in ccid_hc_tx_send_packet

On Mon, Oct 30, 2023 at 4:40 PM Bragatheswaran Manickavel
<bragathemanick0908@...il.com> wrote:
>
>
> On 30/10/23 14:29, Eric Dumazet wrote:
> > On Sat, Oct 28, 2023 at 4:41 PM Bragatheswaran Manickavel
> > <bragathemanick0908@...il.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@...kaller.appspotmail.com
> >> Closes: https://syzkaller.appspot.com/bug?extid=c71bc336c5061153b502
> >> Signed-off-by: Bragatheswaran Manickavel <bragathemanick0908@...il.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 != NULL)
> >> +       if (ccid != NULL && ccid->ccid_ops->ccid_hc_tx_send_packet != 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()
>
>
> Hi Eric,
>
> In both do_dccp_getsockopt() and dccp_get_info(), dccps_hc_rx_ccid are
> checked properly before access.
>

Not really, because another thread can change the value at the same time.

Adding checks is not solving races.