Date:   Thu, 7 Mar 2019 06:59:08 -0500
From:   Neil Horman <nhorman@...driver.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem <davem@...emloft.net>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCH net 1/3] sctp: sctp_sock_migrate() returns error if
 sctp_bind_addr_dup() fails

On Thu, Mar 07, 2019 at 06:06:21PM +0800, Xin Long wrote:
> On Thu, Mar 7, 2019 at 2:21 AM Neil Horman <nhorman@...driver.com> wrote:
> >
> > On Sun, Mar 03, 2019 at 05:54:53PM +0800, Xin Long wrote:
> > > It should fail to create the new sk if sctp_bind_addr_dup() fails
> > > when accepting or peeloff an association.
> > >
> > > Signed-off-by: Xin Long <lucien.xin@...il.com>
> > > ---
> > >  net/sctp/socket.c | 34 ++++++++++++++++++++++++----------
> > >  1 file changed, 24 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > > index a2771b3..22adb8d 100644
> > > --- a/net/sctp/socket.c
> > > +++ b/net/sctp/socket.c
> > > @@ -102,9 +102,9 @@ static int sctp_send_asconf(struct sctp_association *asoc,
> > >                           struct sctp_chunk *chunk);
> > >  static int sctp_do_bind(struct sock *, union sctp_addr *, int);
> > >  static int sctp_autobind(struct sock *sk);
> > > -static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
> > > -                           struct sctp_association *assoc,
> > > -                           enum sctp_socket_type type);
> > > +static int sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
> > > +                          struct sctp_association *assoc,
> > > +                          enum sctp_socket_type type);
> > >
> > >  static unsigned long sctp_memory_pressure;
> > >  static atomic_long_t sctp_memory_allocated;
> > > @@ -4655,7 +4655,11 @@ static struct sock *sctp_accept(struct sock *sk, int flags, int *err, bool kern)
> > >       /* Populate the fields of the newsk from the oldsk and migrate the
> > >        * asoc to the newsk.
> > >        */
> > > -     sctp_sock_migrate(sk, newsk, asoc, SCTP_SOCKET_TCP);
> > > +     error = sctp_sock_migrate(sk, newsk, asoc, SCTP_SOCKET_TCP);
> > > +     if (error) {
> > > +             sk_common_release(newsk);
> > sctp_sock_migrate may fail after the pending packets have been moved from the
> > old socket to the new socket.  Normally those packets will get purged by
> > successful transmission, or when the socket is closed (via sctp_close), but
> > neither of those cases applies here.  Whats going to dequeue and free any
> > pending skbs on the sk_receive_queue here?
> >
> > > +             newsk = NULL;
> > > +     }
> > >
> > >  out:
> > >       release_sock(sk);
> > > @@ -5401,7 +5405,12 @@ int sctp_do_peeloff(struct sock *sk, sctp_assoc_t id, struct socket **sockp)
> > >       /* Populate the fields of the newsk from the oldsk and migrate the
> > >        * asoc to the newsk.
> > >        */
> > > -     sctp_sock_migrate(sk, sock->sk, asoc, SCTP_SOCKET_UDP_HIGH_BANDWIDTH);
> > > +     err = sctp_sock_migrate(sk, sock->sk, asoc,
> > > +                             SCTP_SOCKET_UDP_HIGH_BANDWIDTH);
> > > +     if (err) {
> > > +             sock_release(sock);
> > Same question here, what frees any pending skbs on the new socket, if the
> > migration fails after the skbs have been queued to it?
> Luckily, in sctp_sock_migrate(), it can only fail before the skbs are
> moved to newsk->sk_receive_queue. So when it returns err,
> newsk->sk_receive_queue must be empty.
> 
Yeah, you're right, I misread the location of the check, thinking it came after
the skb migration, this is fine.

> >
> > > +             sock = NULL;
> > > +     }
> > >
> > >       *sockp = sock;
> > >
> > > @@ -8924,9 +8933,9 @@ static inline void sctp_copy_descendant(struct sock *sk_to,
> > >  /* Populate the fields of the newsk from the oldsk and migrate the assoc
> > >   * and its messages to the newsk.
> > >   */
> > > -static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
> > > -                           struct sctp_association *assoc,
> > > -                           enum sctp_socket_type type)
> > > +static int sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
> > > +                          struct sctp_association *assoc,
> > > +                          enum sctp_socket_type type)
> > >  {
> > >       struct sctp_sock *oldsp = sctp_sk(oldsk);
> > >       struct sctp_sock *newsp = sctp_sk(newsk);
> > > @@ -8935,6 +8944,7 @@ static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
> > >       struct sk_buff *skb, *tmp;
> > >       struct sctp_ulpevent *event;
> > >       struct sctp_bind_hashbucket *head;
> > > +     int err;
> > >
> > >       /* Migrate socket buffer sizes and all the socket level options to the
> > >        * new socket.
> > > @@ -8963,8 +8973,10 @@ static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
> > >       /* Copy the bind_addr list from the original endpoint to the new
> > >        * endpoint so that we can handle restarts properly
> > >        */
> > > -     sctp_bind_addr_dup(&newsp->ep->base.bind_addr,
> > > -                             &oldsp->ep->base.bind_addr, GFP_KERNEL);
> > > +     err = sctp_bind_addr_dup(&newsp->ep->base.bind_addr,
> > > +                              &oldsp->ep->base.bind_addr, GFP_KERNEL);
> > > +     if (err)
> > > +             return err;
> > >
> > >       /* Move any messages in the old socket's receive queue that are for the
> > >        * peeled off association to the new socket's receive queue.
> > > @@ -9049,6 +9061,8 @@ static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
> > >       }
> > >
> > >       release_sock(newsk);
> > > +
> > > +     return 0;
> > >  }
> > >
> > >
> > > --
> > > 2.1.0
> > >
> > >
> 

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