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Message-ID: <20240804203346.3654426-11-chopps@chopps.org>
Date: Sun, 4 Aug 2024 16:33:39 -0400
From: Christian Hopps <chopps@...pps.org>
To: devel@...ux-ipsec.org
Cc: Steffen Klassert <steffen.klassert@...unet.com>,
netdev@...r.kernel.org,
Christian Hopps <chopps@...pps.org>,
Christian Hopps <chopps@...n.net>
Subject: [PATCH ipsec-next v8 10/16] xfrm: iptfs: add fragmenting of larger than MTU user packets
From: Christian Hopps <chopps@...n.net>
Add support for tunneling user (inner) packets that are larger than the
tunnel's path MTU (outer) using IP-TFS fragmentation.
Signed-off-by: Christian Hopps <chopps@...n.net>
---
net/xfrm/xfrm_iptfs.c | 407 +++++++++++++++++++++++++++++++++++++++---
1 file changed, 381 insertions(+), 26 deletions(-)
diff --git a/net/xfrm/xfrm_iptfs.c b/net/xfrm/xfrm_iptfs.c
index 20c19894720e..38735e2d64c3 100644
--- a/net/xfrm/xfrm_iptfs.c
+++ b/net/xfrm/xfrm_iptfs.c
@@ -46,12 +46,23 @@
*/
#define IPTFS_DEFAULT_MAX_QUEUE_SIZE (1024 * 10240)
+/* 1) skb->head should be cache aligned.
+ * 2) when resv is for L2 headers (i.e., ethernet) we want the cacheline to
+ * start -16 from data.
+ * 3) when resv is for L3+L2 headers IOW skb->data points at the IPTFS payload
+ * we want data to be cache line aligned so all the pushed headers will be in
+ * another cacheline.
+ */
+#define XFRM_IPTFS_MIN_L3HEADROOM 128
+#define XFRM_IPTFS_MIN_L2HEADROOM (64 + 16)
+#define IPTFS_FRAG_COPY_MAX 256 /* max for copying to create iptfs frags */
#define NSECS_IN_USEC 1000
#define IPTFS_HRTIMER_MODE HRTIMER_MODE_REL_SOFT
/**
* struct xfrm_iptfs_config - configuration for the IPTFS tunnel.
+ * @dont_frag: true to inhibit fragmenting across IPTFS outer packets.
* @pkt_size: size of the outer IP packet. 0 to use interface and MTU discovery,
* otherwise the user specified value.
* @max_queue_size: The maximum number of octets allowed to be queued to be sent
@@ -59,6 +70,7 @@
* packets enqueued.
*/
struct xfrm_iptfs_config {
+ bool dont_frag : 1;
u32 pkt_size; /* outer_packet_size or 0 */
u32 max_queue_size; /* octets */
};
@@ -88,13 +100,71 @@ struct xfrm_iptfs_data {
u32 payload_mtu; /* max payload size */
};
-static u32 iptfs_get_inner_mtu(struct xfrm_state *x, int outer_mtu);
+static u32 __iptfs_get_inner_mtu(struct xfrm_state *x, int outer_mtu);
static enum hrtimer_restart iptfs_delay_timer(struct hrtimer *me);
/* ================= */
/* SK_BUFF Functions */
/* ================= */
+/**
+ * iptfs_alloc_skb() - Allocate a new `skb` using a meta-data template.
+ * @tpl: the template to copy the new `skb`s meta-data from.
+ * @len: the linear length of the head data, zero is fine.
+ * @l3resv: true if reserve needs to support pushing L3 headers
+ *
+ * A new `skb` is allocated and it's meta-data is initialized from `tpl`, the
+ * head data is sized to `len` + reserved space set according to the @l3resv
+ * boolean. When @l3resv is false, resv is XFRM_IPTFS_MIN_L2HEADROOM which
+ * arranges for `skb->data - 16` (etherhdr space) to be the start of a cacheline.
+ * Otherwise, @l3resv is true and resv is either the size of headroom from `tpl` or
+ * XFRM_IPTFS_MIN_L3HEADROOM whichever is greater, which tries to align
+ * skb->data to a cacheline as all headers will be pushed on the previous
+ * cacheline bytes.
+ *
+ * When copying meta-data from the @tpl, the sk_buff->headers are not copied.
+ *
+ * Zero length skbs are allocated when we only need a head skb to hold new
+ * packet headers (basically the mac header) that sit on top of existing shared
+ * packet data.
+ *
+ * Return: the new skb or NULL.
+ */
+static struct sk_buff *iptfs_alloc_skb(struct sk_buff *tpl, u32 len,
+ bool l3resv)
+{
+ struct sk_buff *skb;
+ u32 resv;
+
+ if (!l3resv) {
+ resv = XFRM_IPTFS_MIN_L2HEADROOM;
+ } else {
+ resv = skb_headroom(tpl);
+ if (resv < XFRM_IPTFS_MIN_L3HEADROOM)
+ resv = XFRM_IPTFS_MIN_L3HEADROOM;
+ }
+
+ skb = alloc_skb(len + resv, GFP_ATOMIC);
+ if (!skb) {
+ XFRM_INC_STATS(dev_net(tpl->dev), LINUX_MIB_XFRMNOSKBERROR);
+ return NULL;
+ }
+
+ skb_reserve(skb, resv);
+
+ /* We do not want any of the tpl->headers copied over, so we do
+ * not use `skb_copy_header()`.
+ */
+ skb->tstamp = tpl->tstamp;
+ skb->dev = tpl->dev;
+ memcpy(skb->cb, tpl->cb, sizeof(skb->cb));
+ skb_dst_copy(skb, tpl);
+ __skb_ext_copy(skb, tpl);
+ __nf_copy(skb, tpl, false);
+
+ return skb;
+}
+
/**
* skb_head_to_frag() - initialize a skb_frag_t based on skb head data
* @skb: skb with the head data
@@ -109,6 +179,41 @@ static void skb_head_to_frag(const struct sk_buff *skb, skb_frag_t *frag)
skb_frag_fill_page_desc(frag, page, skb->data - addr, skb_headlen(skb));
}
+/**
+ * skb_copy_bits_seq - copy bits from a skb_seq_state to kernel buffer
+ * @st: source skb_seq_state
+ * @offset: offset in source
+ * @to: destination buffer
+ * @len: number of bytes to copy
+ *
+ * Copy @len bytes from @offset bytes into the source @st to the destination
+ * buffer @to. `offset` should increase (or be unchanged) with each subsequent
+ * call to this function. If offset needs to decrease from the previous use `st`
+ * should be reset first.
+ *
+ * Return: 0 on success or a negative error code on failure
+ */
+static int skb_copy_bits_seq(struct skb_seq_state *st, int offset, void *to,
+ int len)
+{
+ const u8 *data;
+ u32 sqlen;
+
+ for (;;) {
+ sqlen = skb_seq_read(offset, &data, st);
+ if (sqlen == 0)
+ return -ENOMEM;
+ if (sqlen >= len) {
+ memcpy(to, data, len);
+ return 0;
+ }
+ memcpy(to, data, sqlen);
+ to += sqlen;
+ offset += sqlen;
+ len -= sqlen;
+ }
+}
+
/* ================================= */
/* IPTFS Sending (ingress) Functions */
/* ================================= */
@@ -153,7 +258,7 @@ static int iptfs_get_cur_pmtu(struct xfrm_state *x,
{
struct xfrm_dst *xdst = (struct xfrm_dst *)skb_dst(skb);
u32 payload_mtu = xtfs->payload_mtu;
- u32 pmtu = iptfs_get_inner_mtu(x, xdst->child_mtu_cached);
+ u32 pmtu = __iptfs_get_inner_mtu(x, xdst->child_mtu_cached);
if (payload_mtu && payload_mtu < pmtu)
pmtu = payload_mtu;
@@ -216,7 +321,8 @@ static int iptfs_output_collect(struct net *net, struct sock *sk,
BUG_ON(!xtfs);
- pmtu = iptfs_get_cur_pmtu(x, xtfs, skb);
+ if (xtfs->cfg.dont_frag)
+ pmtu = iptfs_get_cur_pmtu(x, xtfs, skb);
/* Break apart GSO skbs. If the queue is nearing full then we want the
* accounting and queuing to be based on the individual packets not on the
@@ -256,8 +362,10 @@ static int iptfs_output_collect(struct net *net, struct sock *sk,
continue;
}
- /* Fragmenting handled in following commits. */
- if (iptfs_is_too_big(sk, skb, pmtu)) {
+ /* If the user indicated no iptfs fragmenting check before
+ * enqueue.
+ */
+ if (xtfs->cfg.dont_frag && iptfs_is_too_big(sk, skb, pmtu)) {
kfree_skb_reason(skb, SKB_DROP_REASON_PKT_TOO_BIG);
continue;
}
@@ -301,6 +409,219 @@ static void iptfs_output_prepare_skb(struct sk_buff *skb, u32 blkoff)
IPCB(skb)->flags |= IPSKB_XFRM_TUNNEL_SIZE;
}
+/**
+ * iptfs_copy_create_frag() - create an inner fragment skb.
+ * @st: The source packet data.
+ * @offset: offset in @st of the new fragment data.
+ * @copy_len: the amount of data to copy from @st.
+ *
+ * Create a new skb holding a single IPTFS inner packet fragment. @copy_len must
+ * not be greater than the max fragment size.
+ *
+ * Return: the new fragment skb or an ERR_PTR().
+ */
+static struct sk_buff *iptfs_copy_create_frag(struct skb_seq_state *st,
+ u32 offset, u32 copy_len)
+{
+ struct sk_buff *src = st->root_skb;
+ struct sk_buff *skb;
+ int err;
+
+ skb = iptfs_alloc_skb(src, copy_len, true);
+ if (!skb)
+ return ERR_PTR(-ENOMEM);
+
+ /* Now copy `copy_len` data from src */
+ err = skb_copy_bits_seq(st, offset, skb_put(skb, copy_len), copy_len);
+ if (err) {
+ kfree_skb(skb);
+ return ERR_PTR(err);
+ }
+
+ return skb;
+}
+
+/**
+ * iptfs_copy_create_frags() - create and send N-1 fragments of a larger skb.
+ * @skbp: the source packet skb (IN), skb holding the last fragment in
+ * the fragment stream (OUT).
+ * @xtfs: IPTFS SA state.
+ * @mtu: the max IPTFS fragment size.
+ *
+ * This function is responsible for fragmenting a larger inner packet into a
+ * sequence of IPTFS payload packets. The last fragment is returned rather than
+ * being sent so that the caller can append more inner packets (aggregation) if
+ * there is room.
+ *
+ * Return: 0 on success or a negative error code on failure
+ */
+static int iptfs_copy_create_frags(struct sk_buff **skbp,
+ struct xfrm_iptfs_data *xtfs, u32 mtu)
+{
+ struct skb_seq_state skbseq;
+ struct list_head sublist;
+ struct sk_buff *skb = *skbp;
+ struct sk_buff *nskb = *skbp;
+ u32 copy_len, offset;
+ u32 to_copy = skb->len - mtu;
+ int err = 0;
+
+ INIT_LIST_HEAD(&sublist);
+
+ BUG_ON(skb->len <= mtu);
+ skb_prepare_seq_read(skb, 0, skb->len, &skbseq);
+
+ /* A trimmed `skb` will be sent as the first fragment, later. */
+ offset = mtu;
+ to_copy = skb->len - offset;
+ while (to_copy) {
+ /* Send all but last fragment to allow agg. append */
+ list_add_tail(&nskb->list, &sublist);
+
+ /* FUTURE: if the packet has an odd/non-aligning length we could
+ * send less data in the penultimate fragment so that the last
+ * fragment then ends on an aligned boundary.
+ */
+ copy_len = min(to_copy, mtu);
+ nskb = iptfs_copy_create_frag(&skbseq, offset, copy_len);
+ if (IS_ERR(nskb)) {
+ XFRM_INC_STATS(xs_net(xtfs->x),
+ LINUX_MIB_XFRMOUTERROR);
+ skb_abort_seq_read(&skbseq);
+ err = PTR_ERR(nskb);
+ nskb = NULL;
+ break;
+ }
+ iptfs_output_prepare_skb(nskb, to_copy);
+ offset += copy_len;
+ to_copy -= copy_len;
+ }
+ skb_abort_seq_read(&skbseq);
+
+ /* return last fragment that will be unsent (or NULL) */
+ *skbp = nskb;
+
+ /* trim the original skb to MTU */
+ if (!err)
+ err = pskb_trim(skb, mtu);
+
+ if (err) {
+ /* Free all frags. Don't bother sending a partial packet we will
+ * never complete.
+ */
+ kfree_skb(nskb);
+ list_for_each_entry_safe(skb, nskb, &sublist, list) {
+ skb_list_del_init(skb);
+ kfree_skb(skb);
+ }
+ return err;
+ }
+
+ /* prepare the initial fragment with an iptfs header */
+ iptfs_output_prepare_skb(skb, 0);
+
+ /* Send all but last fragment, if we fail to send a fragment then free
+ * the rest -- no point in sending a packet that can't be reassembled.
+ */
+ list_for_each_entry_safe(skb, nskb, &sublist, list) {
+ skb_list_del_init(skb);
+ if (!err)
+ err = xfrm_output(NULL, skb);
+ else
+ kfree_skb(skb);
+ }
+ if (err)
+ kfree_skb(*skbp);
+ return err;
+}
+
+/**
+ * iptfs_first_should_copy() - determine if we should copy packet data.
+ * @first_skb: the first skb in the packet
+ * @mtu: the MTU.
+ *
+ * Determine if we should create subsequent skbs to hold the remaining data from
+ * a large inner packet by copying the packet data, or cloning the original skb
+ * and adjusting the offsets.
+ *
+ * Return: true if we should copy the data out of the skb.
+ */
+static bool iptfs_first_should_copy(struct sk_buff *first_skb, u32 mtu)
+{
+ u32 frag_copy_max;
+
+ /* If we have less than frag_copy_max for remaining packet we copy
+ * those tail bytes as it is more efficient.
+ */
+ frag_copy_max = min(mtu, IPTFS_FRAG_COPY_MAX);
+ if ((int)first_skb->len - (int)mtu < (int)frag_copy_max)
+ return true;
+
+ /* If we have non-linear skb just use copy */
+ if (skb_is_nonlinear(first_skb))
+ return true;
+
+ /* So we have a simple linear skb, easy to clone and share */
+ return false;
+}
+
+/**
+ * iptfs_first_skb() - handle the first dequeued inner packet for output
+ * @skbp: the source packet skb (IN), skb holding the last fragment in
+ * the fragment stream (OUT).
+ * @xtfs: IPTFS SA state.
+ * @mtu: the max IPTFS fragment size.
+ *
+ * This function is responsible for fragmenting a larger inner packet into a
+ * sequence of IPTFS payload packets. If it needs to fragment into subsequent
+ * skb's, it will either do so by copying or cloning.
+ *
+ * The last fragment is returned rather than being sent so that the caller can
+ * append more inner packets (aggregation) if there is room.
+ *
+ * Return: 0 on success or a negative error code on failure
+ */
+static int iptfs_first_skb(struct sk_buff **skbp, struct xfrm_iptfs_data *xtfs,
+ u32 mtu)
+{
+ struct sk_buff *skb = *skbp;
+ int err;
+
+ /* Classic ESP skips the don't fragment ICMP error if DF is clear on
+ * the inner packet or ignore_df is set. Otherwise it will send an ICMP
+ * or local error if the inner packet won't fit it's MTU.
+ *
+ * With IPTFS we do not care about the inner packet DF bit. If the
+ * tunnel is configured to "don't fragment" we error back if things
+ * don't fit in our max packet size. Otherwise we iptfs-fragment as
+ * normal.
+ */
+
+ /* The opportunity for HW offload has ended */
+ if (skb->ip_summed == CHECKSUM_PARTIAL) {
+ err = skb_checksum_help(skb);
+ if (err)
+ return err;
+ }
+
+ /* We've split these up before queuing */
+ BUG_ON(skb_is_gso(skb));
+
+ /* Simple case -- it fits. `mtu` accounted for all the overhead
+ * including the basic IPTFS header.
+ */
+ if (skb->len <= mtu) {
+ iptfs_output_prepare_skb(skb, 0);
+ return 0;
+ }
+
+ if (iptfs_first_should_copy(skb, mtu))
+ return iptfs_copy_create_frags(skbp, xtfs, mtu);
+
+ /* For now we always copy */
+ return iptfs_copy_create_frags(skbp, xtfs, mtu);
+}
+
static struct sk_buff **iptfs_rehome_fraglist(struct sk_buff **nextp,
struct sk_buff *child)
{
@@ -360,6 +681,15 @@ static void iptfs_output_queued(struct xfrm_state *x, struct sk_buff_head *list)
struct sk_buff *skb, *skb2, **nextp;
struct skb_shared_info *shi, *shi2;
+ /* If we are fragmenting due to a large inner packet we will output all
+ * the outer IPTFS packets required to contain the fragments of the
+ * single large inner packet. These outer packets need to be sent
+ * consecutively (ESP seq-wise). Since this output function is always
+ * running from a timer we do not need a lock to provide this guarantee.
+ * We will output our packets consecutively before the timer is allowed
+ * to run again on some other CPU.
+ */
+
while ((skb = __skb_dequeue(list))) {
u32 mtu = iptfs_get_cur_pmtu(x, xtfs, skb);
bool share_ok = true;
@@ -370,7 +700,7 @@ static void iptfs_output_queued(struct xfrm_state *x, struct sk_buff_head *list)
htons(ETH_P_IP) :
htons(ETH_P_IPV6);
- if (skb->len > mtu) {
+ if (skb->len > mtu && xtfs->cfg.dont_frag) {
/* We handle this case before enqueueing so we are only
* here b/c MTU changed after we enqueued before we
* dequeued, just drop these.
@@ -381,26 +711,22 @@ static void iptfs_output_queued(struct xfrm_state *x, struct sk_buff_head *list)
continue;
}
- /* If we don't have a cksum in the packet we need to add one
- * before encapsulation.
+ /* Convert first inner packet into an outer IPTFS packet,
+ * dealing with any fragmentation into multiple outer packets
+ * if necessary.
*/
- if (skb->ip_summed == CHECKSUM_PARTIAL) {
- if (skb_checksum_help(skb)) {
- XFRM_INC_STATS(dev_net(skb_dst(skb)->dev),
- LINUX_MIB_XFRMOUTERROR);
- kfree_skb(skb);
- continue;
- }
- }
-
- /* Convert first inner packet into an outer IPTFS packet */
- iptfs_output_prepare_skb(skb, 0);
+ if (iptfs_first_skb(&skb, xtfs, mtu))
+ continue;
- /* The space remaining to send more inner packet data is `mtu` -
- * (skb->len - sizeof iptfs header). This is b/c the `mtu` value
- * has the basic IPTFS header len accounted for, and we added
- * that header to the skb so it is a part of skb->len, thus we
- * subtract it from the skb length.
+ /* If fragmentation was required the returned skb is the last
+ * IPTFS fragment in the chain, and it's IPTFS header blkoff has
+ * been set just past the end of the fragment data.
+ *
+ * In either case the space remaining to send more inner packet
+ * data is `mtu` - (skb->len - sizeof iptfs header). This is b/c
+ * the `mtu` value has the basic IPTFS header len accounted for,
+ * and we added that header to the skb so it is a part of
+ * skb->len, thus we subtract it from the skb length.
*/
remaining = mtu - (skb->len - sizeof(struct ip_iptfs_hdr));
@@ -641,11 +967,13 @@ static int iptfs_prepare_output(struct xfrm_state *x, struct sk_buff *skb)
/* ========================== */
/**
- * iptfs_get_inner_mtu() - return inner MTU with no fragmentation.
+ * __iptfs_get_inner_mtu() - return inner MTU with no fragmentation.
* @x: xfrm state.
* @outer_mtu: the outer mtu
+ *
+ * Return: Correct MTU taking in to account the encap overhead.
*/
-static u32 iptfs_get_inner_mtu(struct xfrm_state *x, int outer_mtu)
+static u32 __iptfs_get_inner_mtu(struct xfrm_state *x, int outer_mtu)
{
struct crypto_aead *aead;
u32 blksize;
@@ -656,6 +984,23 @@ static u32 iptfs_get_inner_mtu(struct xfrm_state *x, int outer_mtu)
~(blksize - 1)) - 2;
}
+/**
+ * iptfs_get_inner_mtu() - return the inner MTU for an IPTFS xfrm.
+ * @x: xfrm state.
+ * @outer_mtu: Outer MTU for the encapsulated packet.
+ *
+ * Return: Correct MTU taking in to account the encap overhead.
+ */
+static u32 iptfs_get_inner_mtu(struct xfrm_state *x, int outer_mtu)
+{
+ struct xfrm_iptfs_data *xtfs = x->mode_data;
+
+ /* If not dont-frag we have no MTU */
+ if (!xtfs->cfg.dont_frag)
+ return x->outer_mode.family == AF_INET ? IP_MAX_MTU : IP6_MAX_MTU;
+ return __iptfs_get_inner_mtu(x, outer_mtu);
+}
+
/**
* iptfs_user_init() - initialize the SA with IPTFS options from netlink.
* @net: the net data
@@ -677,6 +1022,8 @@ static int iptfs_user_init(struct net *net, struct xfrm_state *x,
xc->max_queue_size = IPTFS_DEFAULT_MAX_QUEUE_SIZE;
xtfs->init_delay_ns = IPTFS_DEFAULT_INIT_DELAY_USECS * NSECS_IN_USEC;
+ if (attrs[XFRMA_IPTFS_DONT_FRAG])
+ xc->dont_frag = true;
if (attrs[XFRMA_IPTFS_PKT_SIZE]) {
xc->pkt_size = nla_get_u32(attrs[XFRMA_IPTFS_PKT_SIZE]);
if (!xc->pkt_size) {
@@ -710,6 +1057,8 @@ static unsigned int iptfs_sa_len(const struct xfrm_state *x)
unsigned int l = 0;
if (x->dir == XFRM_SA_DIR_OUT) {
+ if (xc->dont_frag)
+ l += nla_total_size(0); /* dont-frag flag */
l += nla_total_size(sizeof(u32)); /* init delay usec */
l += nla_total_size(sizeof(xc->max_queue_size));
l += nla_total_size(sizeof(xc->pkt_size));
@@ -726,6 +1075,12 @@ static int iptfs_copy_to_user(struct xfrm_state *x, struct sk_buff *skb)
u64 q;
if (x->dir == XFRM_SA_DIR_OUT) {
+ if (xc->dont_frag) {
+ ret = nla_put_flag(skb, XFRMA_IPTFS_DONT_FRAG);
+ if (ret)
+ return ret;
+ }
+
q = xtfs->init_delay_ns;
(void)do_div(q, NSECS_IN_USEC);
ret = nla_put_u32(skb, XFRMA_IPTFS_INIT_DELAY, q);
--
2.46.0
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