From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH v2 net-next 2/2] kcm: Check if sk_user_data already set in kcm_attach Date: Fri, 26 Jan 2018 13:07:58 -0800 Message-ID: <1517000878.3715.61.camel@gmail.com> References: <20180124203541.3172-1-tom@quantonium.net> <20180124203541.3172-3-tom@quantonium.net> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, rohit@quantonium.net, jchapman@katalix.com, g.nault@alphalink.fr To: Tom Herbert , davem@davemloft.net Return-path: Received: from mail-pg0-f65.google.com ([74.125.83.65]:47033 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751534AbeAZVIB (ORCPT ); Fri, 26 Jan 2018 16:08:01 -0500 Received: by mail-pg0-f65.google.com with SMTP id s9so998882pgq.13 for ; Fri, 26 Jan 2018 13:08:01 -0800 (PST) In-Reply-To: <20180124203541.3172-3-tom@quantonium.net> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 2018-01-24 at 12:35 -0800, Tom Herbert wrote: > This is needed to prevent sk_user_data being overwritten. > The check is done under the callback lock. This should prevent > a socket from being attached twice to a KCM mux. It also prevents > a socket from being attached for other use cases of sk_user_data > as long as the other cases set sk_user_data under the lock. > Followup work is needed to unify all the use cases of sk_user_data > to use the same locking. > > Reported-by: syzbot+114b15f2be420a8886c3@syzkaller.appspotmail.com > Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module") > Signed-off-by: Tom Herbert > --- > net/kcm/kcmsock.c | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) > > diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c > index 7632797fb68e..4a8d407f8902 100644 > --- a/net/kcm/kcmsock.c > +++ b/net/kcm/kcmsock.c > @@ -1410,9 +1410,18 @@ static int kcm_attach(struct socket *sock, struct socket *csock, > return err; > } > > - sock_hold(csk); > - > write_lock_bh(&csk->sk_callback_lock); > + > + /* Check if sk_user_data is aready by KCM or someone else. > + * Must be done under lock to prevent race conditions. > + */ > + if (csk->sk_user_data) { > + write_unlock_bh(&csk->sk_callback_lock); > + strp_done(&psock->strp); Although it seems psock->strp->stopped wont be set ? We should hit WARN_ON(!strp->stopped);