Commit f869c912 authored Nov 20, 2014 by Daniel Borkmann Committed by David S. Miller Nov 21, 2014

net: sctp: keep owned chunk in destructor_arg instead of skb->cb



It's just silly to hold the skb destructor argument around inside
skb->cb[] as we currently do in SCTP.

Nowadays, we're sort of cheating on data accounting in the sense
that due to commit 4c3a5bda ("sctp: Don't charge for data in
sndbuf again when transmitting packet"), we orphan the skb already
in the SCTP output path, i.e. giving back charged data memory, 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 generally actually a big
candidate for future rework, imho.)

However, storing the destructor in the cb[] can easily cause issues
should an non sctp_packet_set_owner_w()'ed skb ever escape the SCTP
layer, since cb[] may get overwritten by lower layers and thus can
corrupt the chunk pointer. There are no such issues at present,
but lets keep the chunk in destructor_arg, as this is the actual
purpose for it.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 44c8bc3c

net/sctp/socket.c

+4 −8

Original line number	Diff line number	Diff line
		@@ -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);

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