| Message ID | 1416439266-11396-1-git-send-email-dborkman@redhat.com |
|---|---|
| State | Awaiting Upstream, archived |
| Delegated to: | David Miller |
| Headers | show |
On Thu, Nov 20, 2014 at 12:21:06AM +0100, Daniel Borkmann wrote: > It's just silly to hold the skb destructor argument around inside > skb->cb[] as we currently do in SCTP. > > Though this has been around forever, I'm inclined to say that prior > to 4c3a5bdae293 ("sctp: Don't charge for data in sndbuf again when > transmitting packet") this may well have caused issues as doing so > violates the cb[] usage accross layers; before 4c3a5bdae293-times, > we have charged twice for data, and when destructor kicks in, cb[] > could have been overwritten already by someone else. > > Nowadays, we're sort of cheating on data accounting in the sense > that due to commit 4c3a5bdae293, we orphan the skb already in the > SCTP output path, and use a different destructor only to make sure > the sk doesn't vanish on skb destruction time. Thus, cb[] is still > valid here as we operate within the SCTP layer. It's actually a big > candidate for future rework, imho. > > Anyhow, lets keep the chunk in destructor_arg, as this is the actual > purpose for it so that in future, we don't run into trouble. > > Signed-off-by: Daniel Borkmann <dborkman@redhat.com> > --- > net/sctp/socket.c | 12 ++++-------- > 1 file changed, 4 insertions(+), 8 deletions(-) > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c > index 2120292..85e0b65 100644 > --- a/net/sctp/socket.c > +++ b/net/sctp/socket.c > @@ -162,7 +162,7 @@ static inline void sctp_set_owner_w(struct sctp_chunk *chunk) > > chunk->skb->destructor = sctp_wfree; > /* Save the chunk pointer in skb for sctp_wfree to use later. */ > - *((struct sctp_chunk **)(chunk->skb->cb)) = chunk; > + skb_shinfo(chunk->skb)->destructor_arg = chunk; > > asoc->sndbuf_used += SCTP_DATA_SNDSIZE(chunk) + > sizeof(struct sk_buff) + > @@ -6870,14 +6870,10 @@ static void sctp_wake_up_waiters(struct sock *sk, > */ > static void sctp_wfree(struct sk_buff *skb) > { > - struct sctp_association *asoc; > - struct sctp_chunk *chunk; > - struct sock *sk; > + struct sctp_chunk *chunk = skb_shinfo(skb)->destructor_arg; > + struct sctp_association *asoc = chunk->asoc; > + struct sock *sk = asoc->base.sk; > > - /* Get the saved chunk pointer. */ > - chunk = *((struct sctp_chunk **)(skb->cb)); > - asoc = chunk->asoc; > - sk = asoc->base.sk; > asoc->sndbuf_used -= SCTP_DATA_SNDSIZE(chunk) + > sizeof(struct sk_buff) + > sizeof(struct sctp_chunk); > -- > 1.7.11.7 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-sctp" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Seems reasonable Acked-by: Neil Horman <nhorman@tuxdriver.com> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/sctp/socket.c b/net/sctp/socket.c index 2120292..85e0b65 100644 --- a/net/sctp/socket.c +++ b/net/sctp/socket.c @@ -162,7 +162,7 @@ static inline void sctp_set_owner_w(struct sctp_chunk *chunk) chunk->skb->destructor = sctp_wfree; /* Save the chunk pointer in skb for sctp_wfree to use later. */ - *((struct sctp_chunk **)(chunk->skb->cb)) = chunk; + skb_shinfo(chunk->skb)->destructor_arg = chunk; asoc->sndbuf_used += SCTP_DATA_SNDSIZE(chunk) + sizeof(struct sk_buff) + @@ -6870,14 +6870,10 @@ static void sctp_wake_up_waiters(struct sock *sk, */ static void sctp_wfree(struct sk_buff *skb) { - struct sctp_association *asoc; - struct sctp_chunk *chunk; - struct sock *sk; + struct sctp_chunk *chunk = skb_shinfo(skb)->destructor_arg; + struct sctp_association *asoc = chunk->asoc; + struct sock *sk = asoc->base.sk; - /* Get the saved chunk pointer. */ - chunk = *((struct sctp_chunk **)(skb->cb)); - asoc = chunk->asoc; - sk = asoc->base.sk; asoc->sndbuf_used -= SCTP_DATA_SNDSIZE(chunk) + sizeof(struct sk_buff) + sizeof(struct sctp_chunk);
It's just silly to hold the skb destructor argument around inside skb->cb[] as we currently do in SCTP. Though this has been around forever, I'm inclined to say that prior to 4c3a5bdae293 ("sctp: Don't charge for data in sndbuf again when transmitting packet") this may well have caused issues as doing so violates the cb[] usage accross layers; before 4c3a5bdae293-times, we have charged twice for data, and when destructor kicks in, cb[] could have been overwritten already by someone else. Nowadays, we're sort of cheating on data accounting in the sense that due to commit 4c3a5bdae293, we orphan the skb already in the SCTP output path, and use a different destructor only to make sure the sk doesn't vanish on skb destruction time. Thus, cb[] is still valid here as we operate within the SCTP layer. It's actually a big candidate for future rework, imho. Anyhow, lets keep the chunk in destructor_arg, as this is the actual purpose for it so that in future, we don't run into trouble. Signed-off-by: Daniel Borkmann <dborkman@redhat.com> --- net/sctp/socket.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-)