Commit 2013c7e3 authored by Gerrit Renker's avatar Gerrit Renker
Browse files

dccp ccid-3: Fix error in loss detection 



The TFRC loss detection code used the wrong loss condition (RFC 4340, 7.7.1):
 * the difference between sequence numbers s1 and s2 instead of 
 * the number of packets missing between s1 and s2 (one less than the distance).

Since this condition appears in many places of the code, it has been put into a
separate function, dccp_loss_free().

Further changes:
----------------
 * tidied up incorrect typing (it was using `int' for u64/s64 types);
 * optimised conditional statements for common case of non-reordered packets;
 * rewrote comments/documentation to match the changes.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
parent 79d16385

net/dccp/ccids/lib/packet_history.c

+28 −45
Original line number Diff line number Diff line
@@ -215,22 +215,19 @@ static void __one_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n2 
	u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,

	    s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,

	    s2 = DCCP_SKB_CB(skb)->dccpd_seq;

	int n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp,

	   d12 = dccp_delta_seqno(s1, s2), d2;



	if (d12 > 0) {			/* S1  <  S2 */

	if (likely(dccp_delta_seqno(s1, s2) > 0)) {	/* S1  <  S2 */

		h->loss_count = 2;

		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n2);

		return;

	}



	/* S0  <  S2  <  S1 */

	d2 = dccp_delta_seqno(s0, s2);



	if (d2 == 1 || n2 >= d2) {	/* S2 is direct successor of S0 */

		int d21 = -d12;

	if (dccp_loss_free(s0, s2, n2)) {

		u64 n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp;



		if (d21 == 1 || n1 >= d21) {

		if (dccp_loss_free(s2, s1, n1)) {

			/* hole is filled: S0, S2, and S1 are consecutive */

			h->loss_count = 0;

			h->loss_start = tfrc_rx_hist_index(h, 1);
@@ -238,9 +235,9 @@ static void __one_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n2 
			/* gap between S2 and S1: just update loss_prev */

			tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n2);



	} else {			/* hole between S0 and S2 */

	} else {	/* gap between S0 and S2 */

		/*

		 * Reorder history to insert S2 between S0 and s1

		 * Reorder history to insert S2 between S0 and S1

		 */

		tfrc_rx_hist_swap(h, 0, 3);

		h->loss_start = tfrc_rx_hist_index(h, 3);
@@ -256,22 +253,18 @@ static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3) 
	    s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,

	    s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,

	    s3 = DCCP_SKB_CB(skb)->dccpd_seq;

	int n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp,

	   d23 = dccp_delta_seqno(s2, s3), d13, d3, d31;



	if (d23 > 0) {			/* S2  <  S3 */

	if (likely(dccp_delta_seqno(s2, s3) > 0)) {	/* S2  <  S3 */

		h->loss_count = 3;

		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 3), skb, n3);

		return 1;

	}



	/* S3  <  S2 */

	d13 = dccp_delta_seqno(s1, s3);



	if (d13 > 0) {

	if (dccp_delta_seqno(s1, s3) > 0) {		/* S1  <  S3  <  S2 */

		/*

		 * The sequence number order is S1, S3, S2

		 * Reorder history to insert entry between S1 and S2

		 * Reorder history to insert S3 between S1 and S2

		 */

		tfrc_rx_hist_swap(h, 2, 3);

		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n3);
@@ -280,17 +273,15 @@ static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3) 
	}



	/* S0  <  S3  <  S1 */

	d31 = -d13;

	d3  = dccp_delta_seqno(s0, s3);



	if (d3 == 1 || n3 >= d3) {	/* S3 is a successor of S0 */

	if (dccp_loss_free(s0, s3, n3)) {

		u64 n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp;



		if (d31 == 1 || n1 >= d31) {

		if (dccp_loss_free(s3, s1, n1)) {

			/* hole between S0 and S1 filled by S3 */

			int  d2 = dccp_delta_seqno(s1, s2),

			     n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp;

			u64 n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp;



			if (d2 == 1 || n2 >= d2) {

			if (dccp_loss_free(s1, s2, n2)) {

				/* entire hole filled by S0, S3, S1, S2 */

				h->loss_start = tfrc_rx_hist_index(h, 2);

				h->loss_count = 0;
@@ -307,8 +298,8 @@ static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3) 
	}



	/*

	 * The remaining case: S3 is not a successor of S0.

	 * Sequence order is S0, S3, S1, S2; reorder to insert between S0 and S1

	 * The remaining case:  S0  <  S3  <  S1  <  S2;  gap between S0 and S3

	 * Reorder history to insert S3 between S0 and S1.

	 */

	tfrc_rx_hist_swap(h, 0, 3);

	h->loss_start = tfrc_rx_hist_index(h, 3);
@@ -318,33 +309,25 @@ static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3) 
	return 1;

}



/* return the signed modulo-2^48 sequence number distance from entry e1 to e2 */

static s64 tfrc_rx_hist_delta_seqno(struct tfrc_rx_hist *h, u8 e1, u8 e2)

{

	DCCP_BUG_ON(e1 > h->loss_count || e2 > h->loss_count);



	return dccp_delta_seqno(tfrc_rx_hist_entry(h, e1)->tfrchrx_seqno,

				tfrc_rx_hist_entry(h, e2)->tfrchrx_seqno);

}



/* recycle RX history records to continue loss detection if necessary */

static void __three_after_loss(struct tfrc_rx_hist *h)

{

	/*

	 * The distance between S0 and S1 is always greater than 1 and the NDP

	 * count of S1 is smaller than this distance. Otherwise there would

	 * have been no loss. Hence it is only necessary to see whether there

	 * are further missing data packets between S1/S2 and S2/S3.

	 * At this stage we know already that there is a gap between S0 and S1

	 * (since S0 was the highest sequence number received before detecting

	 * the loss). To recycle the loss record, it is	thus only necessary to

	 * check for other possible gaps between S1/S2 and between S2/S3.

	 */

	int d2 = tfrc_rx_hist_delta_seqno(h, 1, 2),

	    d3 = tfrc_rx_hist_delta_seqno(h, 2, 3),

	    n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp,

	u64 s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,

	    s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,

	    s3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_seqno;

	u64 n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp,

	    n3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_ndp;



	if (d2 == 1 || n2 >= d2) {	/* S2 is successor to S1 */

	if (dccp_loss_free(s1, s2, n2)) {



		if (d3 == 1 || n3 >= d3) {

			/* S3 is successor of S2: entire hole is filled */

		if (dccp_loss_free(s2, s3, n3)) {

			/* no gap between S2 and S3: entire hole is filled */

			h->loss_start = tfrc_rx_hist_index(h, 3);

			h->loss_count = 0;

		} else {

net/dccp/dccp.h

+15 −0
Original line number Diff line number Diff line
@@ -153,6 +153,21 @@ static inline u64 max48(const u64 seq1, const u64 seq2) 
	return after48(seq1, seq2) ? seq1 : seq2;

}



/**

 * dccp_loss_free  -  Evaluates condition for data loss from RFC 4340, 7.7.1

 * @s1:	 start sequence number

 * @s2:  end sequence number

 * @ndp: NDP count on packet with sequence number @s2

 * Returns true if the sequence range s1...s2 has no data loss.

 */

static inline bool dccp_loss_free(const u64 s1, const u64 s2, const u64 ndp)

{

	s64 delta = dccp_delta_seqno(s1, s2);



	BUG_TRAP(delta >= 0);

	return (u64)delta <= ndp + 1;

}



enum {

	DCCP_MIB_NUM = 0,

	DCCP_MIB_ACTIVEOPENS,			/* ActiveOpens */

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