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Subject[PATCH 4.19 27/96] net: IP6 defrag: use rbtrees in nf_conntrack_reasm.c
Date
[ Upstream commit 997dd96471641e147cb2c33ad54284000d0f5e35 ]

Currently, IPv6 defragmentation code drops non-last fragments that
are smaller than 1280 bytes: see
commit 0ed4229b08c1 ("ipv6: defrag: drop non-last frags smaller than min mtu")

This behavior is not specified in IPv6 RFCs and appears to break
compatibility with some IPv6 implemenations, as reported here:
https://www.spinics.net/lists/netdev/msg543846.html

This patch re-uses common IP defragmentation queueing and reassembly
code in IP6 defragmentation in nf_conntrack, removing the 1280 byte
restriction.

Signed-off-by: Peter Oskolkov <posk@google.com>
Reported-by: Tom Herbert <tom@herbertland.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv6/netfilter/nf_conntrack_reasm.c | 260 +++++++-----------------
1 file changed, 71 insertions(+), 189 deletions(-)

diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 043ed8eb0ab9..cb1b4772dac0 100644
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -136,6 +136,9 @@ static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
}
#endif

+static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
+ struct sk_buff *prev_tail, struct net_device *dev);
+
static inline u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
{
return 1 << (ipv6_get_dsfield(ipv6h) & INET_ECN_MASK);
@@ -177,9 +180,10 @@ static struct frag_queue *fq_find(struct net *net, __be32 id, u32 user,
static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
const struct frag_hdr *fhdr, int nhoff)
{
- struct sk_buff *prev, *next;
unsigned int payload_len;
- int offset, end;
+ struct net_device *dev;
+ struct sk_buff *prev;
+ int offset, end, err;
u8 ecn;

if (fq->q.flags & INET_FRAG_COMPLETE) {
@@ -254,55 +258,18 @@ static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
goto err;
}

- /* Find out which fragments are in front and at the back of us
- * in the chain of fragments so far. We must know where to put
- * this fragment, right?
- */
- prev = fq->q.fragments_tail;
- if (!prev || prev->ip_defrag_offset < offset) {
- next = NULL;
- goto found;
- }
- prev = NULL;
- for (next = fq->q.fragments; next != NULL; next = next->next) {
- if (next->ip_defrag_offset >= offset)
- break; /* bingo! */
- prev = next;
- }
-
-found:
- /* RFC5722, Section 4:
- * When reassembling an IPv6 datagram, if
- * one or more its constituent fragments is determined to be an
- * overlapping fragment, the entire datagram (and any constituent
- * fragments, including those not yet received) MUST be silently
- * discarded.
- */
-
- /* Check for overlap with preceding fragment. */
- if (prev &&
- (prev->ip_defrag_offset + prev->len) > offset)
- goto discard_fq;
-
- /* Look for overlap with succeeding segment. */
- if (next && next->ip_defrag_offset < end)
- goto discard_fq;
-
- /* Note : skb->ip_defrag_offset and skb->dev share the same location */
- if (skb->dev)
- fq->iif = skb->dev->ifindex;
+ /* Note : skb->rbnode and skb->dev share the same location. */
+ dev = skb->dev;
/* Makes sure compiler wont do silly aliasing games */
barrier();
- skb->ip_defrag_offset = offset;

- /* Insert this fragment in the chain of fragments. */
- skb->next = next;
- if (!next)
- fq->q.fragments_tail = skb;
- if (prev)
- prev->next = skb;
- else
- fq->q.fragments = skb;
+ prev = fq->q.fragments_tail;
+ err = inet_frag_queue_insert(&fq->q, skb, offset, end);
+ if (err)
+ goto insert_error;
+
+ if (dev)
+ fq->iif = dev->ifindex;

fq->q.stamp = skb->tstamp;
fq->q.meat += skb->len;
@@ -319,11 +286,25 @@ static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
fq->q.flags |= INET_FRAG_FIRST_IN;
}

- return 0;
+ if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
+ fq->q.meat == fq->q.len) {
+ unsigned long orefdst = skb->_skb_refdst;
+
+ skb->_skb_refdst = 0UL;
+ err = nf_ct_frag6_reasm(fq, skb, prev, dev);
+ skb->_skb_refdst = orefdst;
+ return err;
+ }
+
+ skb_dst_drop(skb);
+ return -EINPROGRESS;

-discard_fq:
+insert_error:
+ if (err == IPFRAG_DUP)
+ goto err;
inet_frag_kill(&fq->q);
err:
+ skb_dst_drop(skb);
return -EINVAL;
}

@@ -333,147 +314,67 @@ static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
* It is called with locked fq, and caller must check that
* queue is eligible for reassembly i.e. it is not COMPLETE,
* the last and the first frames arrived and all the bits are here.
- *
- * returns true if *prev skb has been transformed into the reassembled
- * skb, false otherwise.
*/
-static bool
-nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *prev, struct net_device *dev)
+static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
+ struct sk_buff *prev_tail, struct net_device *dev)
{
- struct sk_buff *fp, *head = fq->q.fragments;
- int payload_len, delta;
+ void *reasm_data;
+ int payload_len;
u8 ecn;

inet_frag_kill(&fq->q);

- WARN_ON(head == NULL);
- WARN_ON(head->ip_defrag_offset != 0);
-
ecn = ip_frag_ecn_table[fq->ecn];
if (unlikely(ecn == 0xff))
- return false;
+ goto err;
+
+ reasm_data = inet_frag_reasm_prepare(&fq->q, skb, prev_tail);
+ if (!reasm_data)
+ goto err;

- /* Unfragmented part is taken from the first segment. */
- payload_len = ((head->data - skb_network_header(head)) -
+ payload_len = ((skb->data - skb_network_header(skb)) -
sizeof(struct ipv6hdr) + fq->q.len -
sizeof(struct frag_hdr));
if (payload_len > IPV6_MAXPLEN) {
net_dbg_ratelimited("nf_ct_frag6_reasm: payload len = %d\n",
payload_len);
- return false;
- }
-
- delta = - head->truesize;
-
- /* Head of list must not be cloned. */
- if (skb_unclone(head, GFP_ATOMIC))
- return false;
-
- delta += head->truesize;
- if (delta)
- add_frag_mem_limit(fq->q.net, delta);
-
- /* If the first fragment is fragmented itself, we split
- * it to two chunks: the first with data and paged part
- * and the second, holding only fragments. */
- if (skb_has_frag_list(head)) {
- struct sk_buff *clone;
- int i, plen = 0;
-
- clone = alloc_skb(0, GFP_ATOMIC);
- if (clone == NULL)
- return false;
-
- clone->next = head->next;
- head->next = clone;
- skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
- skb_frag_list_init(head);
- for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
- plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
- clone->len = clone->data_len = head->data_len - plen;
- head->data_len -= clone->len;
- head->len -= clone->len;
- clone->csum = 0;
- clone->ip_summed = head->ip_summed;
-
- add_frag_mem_limit(fq->q.net, clone->truesize);
- }
-
- /* morph head into last received skb: prev.
- *
- * This allows callers of ipv6 conntrack defrag to continue
- * to use the last skb(frag) passed into the reasm engine.
- * The last skb frag 'silently' turns into the full reassembled skb.
- *
- * Since prev is also part of q->fragments we have to clone it first.
- */
- if (head != prev) {
- struct sk_buff *iter;
-
- fp = skb_clone(prev, GFP_ATOMIC);
- if (!fp)
- return false;
-
- fp->next = prev->next;
-
- iter = head;
- while (iter) {
- if (iter->next == prev) {
- iter->next = fp;
- break;
- }
- iter = iter->next;
- }
-
- skb_morph(prev, head);
- prev->next = head->next;
- consume_skb(head);
- head = prev;
+ goto err;
}

/* We have to remove fragment header from datagram and to relocate
* header in order to calculate ICV correctly. */
- skb_network_header(head)[fq->nhoffset] = skb_transport_header(head)[0];
- memmove(head->head + sizeof(struct frag_hdr), head->head,
- (head->data - head->head) - sizeof(struct frag_hdr));
- head->mac_header += sizeof(struct frag_hdr);
- head->network_header += sizeof(struct frag_hdr);
-
- skb_shinfo(head)->frag_list = head->next;
- skb_reset_transport_header(head);
- skb_push(head, head->data - skb_network_header(head));
-
- for (fp = head->next; fp; fp = fp->next) {
- head->data_len += fp->len;
- head->len += fp->len;
- if (head->ip_summed != fp->ip_summed)
- head->ip_summed = CHECKSUM_NONE;
- else if (head->ip_summed == CHECKSUM_COMPLETE)
- head->csum = csum_add(head->csum, fp->csum);
- head->truesize += fp->truesize;
- fp->sk = NULL;
- }
- sub_frag_mem_limit(fq->q.net, head->truesize);
+ skb_network_header(skb)[fq->nhoffset] = skb_transport_header(skb)[0];
+ memmove(skb->head + sizeof(struct frag_hdr), skb->head,
+ (skb->data - skb->head) - sizeof(struct frag_hdr));
+ skb->mac_header += sizeof(struct frag_hdr);
+ skb->network_header += sizeof(struct frag_hdr);
+
+ skb_reset_transport_header(skb);
+
+ inet_frag_reasm_finish(&fq->q, skb, reasm_data);

- head->ignore_df = 1;
- head->next = NULL;
- head->dev = dev;
- head->tstamp = fq->q.stamp;
- ipv6_hdr(head)->payload_len = htons(payload_len);
- ipv6_change_dsfield(ipv6_hdr(head), 0xff, ecn);
- IP6CB(head)->frag_max_size = sizeof(struct ipv6hdr) + fq->q.max_size;
+ skb->ignore_df = 1;
+ skb->dev = dev;
+ ipv6_hdr(skb)->payload_len = htons(payload_len);
+ ipv6_change_dsfield(ipv6_hdr(skb), 0xff, ecn);
+ IP6CB(skb)->frag_max_size = sizeof(struct ipv6hdr) + fq->q.max_size;

/* Yes, and fold redundant checksum back. 8) */
- if (head->ip_summed == CHECKSUM_COMPLETE)
- head->csum = csum_partial(skb_network_header(head),
- skb_network_header_len(head),
- head->csum);
+ if (skb->ip_summed == CHECKSUM_COMPLETE)
+ skb->csum = csum_partial(skb_network_header(skb),
+ skb_network_header_len(skb),
+ skb->csum);

fq->q.fragments = NULL;
fq->q.rb_fragments = RB_ROOT;
fq->q.fragments_tail = NULL;
+ fq->q.last_run_head = NULL;

- return true;
+ return 0;
+
+err:
+ inet_frag_kill(&fq->q);
+ return -EINVAL;
}

/*
@@ -542,7 +443,6 @@ find_prev_fhdr(struct sk_buff *skb, u8 *prevhdrp, int *prevhoff, int *fhoff)
int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
{
u16 savethdr = skb->transport_header;
- struct net_device *dev = skb->dev;
int fhoff, nhoff, ret;
struct frag_hdr *fhdr;
struct frag_queue *fq;
@@ -565,10 +465,6 @@ int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
hdr = ipv6_hdr(skb);
fhdr = (struct frag_hdr *)skb_transport_header(skb);

- if (skb->len - skb_network_offset(skb) < IPV6_MIN_MTU &&
- fhdr->frag_off & htons(IP6_MF))
- return -EINVAL;
-
skb_orphan(skb);
fq = fq_find(net, fhdr->identification, user, hdr,
skb->dev ? skb->dev->ifindex : 0);
@@ -580,31 +476,17 @@ int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
spin_lock_bh(&fq->q.lock);

ret = nf_ct_frag6_queue(fq, skb, fhdr, nhoff);
- if (ret < 0) {
- if (ret == -EPROTO) {
- skb->transport_header = savethdr;
- ret = 0;
- }
- goto out_unlock;
+ if (ret == -EPROTO) {
+ skb->transport_header = savethdr;
+ ret = 0;
}

/* after queue has assumed skb ownership, only 0 or -EINPROGRESS
* must be returned.
*/
- ret = -EINPROGRESS;
- if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
- fq->q.meat == fq->q.len) {
- unsigned long orefdst = skb->_skb_refdst;
-
- skb->_skb_refdst = 0UL;
- if (nf_ct_frag6_reasm(fq, skb, dev))
- ret = 0;
- skb->_skb_refdst = orefdst;
- } else {
- skb_dst_drop(skb);
- }
+ if (ret)
+ ret = -EINPROGRESS;

-out_unlock:
spin_unlock_bh(&fq->q.lock);
inet_frag_put(&fq->q);
return ret;
--
2.19.1


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