On Wed, Sep 11, 2019 at 5:03 PM David Laight <David.Laight@xxxxxxxxxx> wrote: > > From: Xin Long [mailto:lucien.xin@xxxxxxxxx] > > Sent: 11 September 2019 09:52 > > On Tue, Sep 10, 2019 at 9:19 PM David Laight <David.Laight@xxxxxxxxxx> wrote: > > > > > > From: Xin Long > > > > Sent: 09 September 2019 08:57 > > > > Section 7.2 of rfc7829: "Peer Address Thresholds (SCTP_PEER_ADDR_THLDS) > > > > Socket Option" extends 'struct sctp_paddrthlds' with 'spt_pathcpthld' > > > > added to allow a user to change ps_retrans per sock/asoc/transport, as > > > > other 2 paddrthlds: pf_retrans, pathmaxrxt. > > > > > > > > Note that ps_retrans is not allowed to be greater than pf_retrans. > > > > > > > > Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx> > > > > --- > > > > include/uapi/linux/sctp.h | 1 + > > > > net/sctp/socket.c | 10 ++++++++++ > > > > 2 files changed, 11 insertions(+) > > > > > > > > diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h > > > > index a15cc28..dfd81e1 100644 > > > > --- a/include/uapi/linux/sctp.h > > > > +++ b/include/uapi/linux/sctp.h > > > > @@ -1069,6 +1069,7 @@ struct sctp_paddrthlds { > > > > struct sockaddr_storage spt_address; > > > > __u16 spt_pathmaxrxt; > > > > __u16 spt_pathpfthld; > > > > + __u16 spt_pathcpthld; > > > > }; > > > > > > > > /* > > > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c > > > > index 5e2098b..5b9774d 100644 > > > > --- a/net/sctp/socket.c > > > > +++ b/net/sctp/socket.c > > > > @@ -3954,6 +3954,9 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk, > > > > > > This code does: > > > if (optlen < sizeof(struct sctp_paddrthlds)) > > > return -EINVAL; > > here will become: > > > > if (optlen >= sizeof(struct sctp_paddrthlds)) { > > optlen = sizeof(struct sctp_paddrthlds); > > } else if (optlen >= ALIGN(offsetof(struct sctp_paddrthlds, > > spt_pathcpthld), 4)) > > optlen = ALIGN(offsetof(struct sctp_paddrthlds, > > spt_pathcpthld), 4); > > val.spt_pathcpthld = 0xffff; > > else { > > return -EINVAL; > > } > > Hmmm... > If the kernel has to default 'val.spt_pathcpthld = 0xffff' > then recompiling an existing application with the new uapi > header is going to lead to very unexpected behaviour. > > The best you can hope for is that the application memset the > structure to zero. > But more likely it is 'random' on-stack data. 0xffff is a value to disable the feature 'Primary Path Switchover'. you're right that user might set it to zero unexpectly with their old application rebuilt. A safer way is to introduce "sysctl net.sctp.ps_retrans", it won't matter if users set spt_pathcpthld properly when they're not aware of this feature, like "sysctl net.sctp.pF_retrans". Looks better? > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales)
