[PATCH 4.14 58/70] net: IP6 defrag: use rbtrees for IPv6 defrag

Greg Kroah-Hartman
2019-04-24T17:51:47Z

[ Upstream commit d4289fcc9b16b89619ee1c54f829e05e56de8b9a ]

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 IPv6, removing the 1280 byte restriction.

v2: change handling of overlaps to match that of upstream.

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>
---
include/net/ipv6_frag.h | 11 +-
net/ipv6/reassembly.c | 249 +++++++++++-----------------------------
2 files changed, 77 insertions(+), 183 deletions(-)

diff --git a/include/net/ipv6_frag.h b/include/net/ipv6_frag.h
index 6ced1e6899b6..28aa9b30aece 100644
--- a/include/net/ipv6_frag.h
+++ b/include/net/ipv6_frag.h
@@ -82,8 +82,15 @@ ip6frag_expire_frag_queue(struct net *net, struct frag_queue *fq)
__IP6_INC_STATS(net, __in6_dev_get(dev), IPSTATS_MIB_REASMTIMEOUT);

/* Don't send error if the first segment did not arrive. */
- head = fq->q.fragments;
- if (!(fq->q.flags & INET_FRAG_FIRST_IN) || !head)
+ if (!(fq->q.flags & INET_FRAG_FIRST_IN))
+ goto out;
+
+ /* sk_buff::dev and sk_buff::rbnode are unionized. So we
+ * pull the head out of the tree in order to be able to
+ * deal with head->dev.
+ */
+ head = inet_frag_pull_head(&fq->q);
+ if (!head)
goto out;

head->dev = dev;
diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index e5ab3b7813d6..fe797b29ca89 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -62,13 +62,6 @@

static const char ip6_frag_cache_name[] = "ip6-frags";

-struct ip6frag_skb_cb {
- struct inet6_skb_parm h;
- int offset;
-};
-
-#define FRAG6_CB(skb) ((struct ip6frag_skb_cb *)((skb)->cb))
-
static u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
{
return 1 << (ipv6_get_dsfield(ipv6h) & INET_ECN_MASK);
@@ -76,8 +69,8 @@ static u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)

static struct inet_frags ip6_frags;

-static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
- struct net_device *dev);
+static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *skb,
+ struct sk_buff *prev_tail, struct net_device *dev);

static void ip6_frag_expire(struct timer_list *t)
{
@@ -118,21 +111,26 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
struct frag_hdr *fhdr, int nhoff,
u32 *prob_offset)
{
- struct sk_buff *prev, *next;
- struct net_device *dev;
- int offset, end, fragsize;
struct net *net = dev_net(skb_dst(skb)->dev);
+ int offset, end, fragsize;
+ struct sk_buff *prev_tail;
+ struct net_device *dev;
+ int err = -ENOENT;
u8 ecn;

if (fq->q.flags & INET_FRAG_COMPLETE)
goto err;

+ err = -EINVAL;
offset = ntohs(fhdr->frag_off) & ~0x7;
end = offset + (ntohs(ipv6_hdr(skb)->payload_len) -
((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));

if ((unsigned int)end > IPV6_MAXPLEN) {
*prob_offset = (u8 *)&fhdr->frag_off - skb_network_header(skb);
+ /* note that if prob_offset is set, the skb is freed elsewhere,
+ * we do not free it here.
+ */
return -1;
}

@@ -152,7 +150,7 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
*/
if (end < fq->q.len ||
((fq->q.flags & INET_FRAG_LAST_IN) && end != fq->q.len))
- goto err;
+ goto discard_fq;
fq->q.flags |= INET_FRAG_LAST_IN;
fq->q.len = end;
} else {
@@ -169,70 +167,36 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
if (end > fq->q.len) {
/* Some bits beyond end -> corruption. */
if (fq->q.flags & INET_FRAG_LAST_IN)
- goto err;
+ goto discard_fq;
fq->q.len = end;
}
}

if (end == offset)
- goto err;
+ goto discard_fq;

+ err = -ENOMEM;
/* Point into the IP datagram 'data' part. */
if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data))
- goto err;
-
- if (pskb_trim_rcsum(skb, end - offset))
- 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 || FRAG6_CB(prev)->offset < offset) {
- next = NULL;
- goto found;
- }
- prev = NULL;
- for (next = fq->q.fragments; next != NULL; next = next->next) {
- if (FRAG6_CB(next)->offset >= offset)
- break; /* bingo! */
- prev = next;
- }
-
-found:
- /* RFC5722, Section 4, amended by Errata ID : 3089
- * 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) MUST be silently discarded.
- */
-
- /* Check for overlap with preceding fragment. */
- if (prev &&
- (FRAG6_CB(prev)->offset + prev->len) > offset)
goto discard_fq;

- /* Look for overlap with succeeding segment. */
- if (next && FRAG6_CB(next)->offset < end)
+ err = pskb_trim_rcsum(skb, end - offset);
+ if (err)
goto discard_fq;

- FRAG6_CB(skb)->offset = offset;
+ /* Note : skb->rbnode and skb->dev share the same location. */
+ dev = skb->dev;
+ /* Makes sure compiler wont do silly aliasing games */
+ barrier();

- /* 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_tail = fq->q.fragments_tail;
+ err = inet_frag_queue_insert(&fq->q, skb, offset, end);
+ if (err)
+ goto insert_error;

- dev = skb->dev;
- if (dev) {
+ if (dev)
fq->iif = dev->ifindex;
- skb->dev = NULL;
- }
+
fq->q.stamp = skb->tstamp;
fq->q.meat += skb->len;
fq->ecn |= ecn;
@@ -252,44 +216,48 @@ found:

if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
fq->q.meat == fq->q.len) {
- int res;
unsigned long orefdst = skb->_skb_refdst;

skb->_skb_refdst = 0UL;
- res = ip6_frag_reasm(fq, prev, dev);
+ err = ip6_frag_reasm(fq, skb, prev_tail, dev);
skb->_skb_refdst = orefdst;
- return res;
+ return err;
}

skb_dst_drop(skb);
- return -1;
+ return -EINPROGRESS;

+insert_error:
+ if (err == IPFRAG_DUP) {
+ kfree_skb(skb);
+ return -EINVAL;
+ }
+ err = -EINVAL;
+ __IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
+ IPSTATS_MIB_REASM_OVERLAPS);
discard_fq:
inet_frag_kill(&fq->q);
-err:
__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
IPSTATS_MIB_REASMFAILS);
+err:
kfree_skb(skb);
- return -1;
+ return err;
}

/*
* Check if this packet is complete.
- * Returns NULL on failure by any reason, and pointer
- * to current nexthdr field in reassembled frame.
*
* 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.
*/
-static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
- struct net_device *dev)
+static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *skb,
+ struct sk_buff *prev_tail, struct net_device *dev)
{
struct net *net = container_of(fq->q.net, struct net, ipv6.frags);
- struct sk_buff *fp, *head = fq->q.fragments;
- int payload_len, delta;
unsigned int nhoff;
- int sum_truesize;
+ void *reasm_data;
+ int payload_len;
u8 ecn;

inet_frag_kill(&fq->q);
@@ -298,120 +266,40 @@ static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
if (unlikely(ecn == 0xff))
goto out_fail;

- /* Make the one we just received the head. */
- if (prev) {
- head = prev->next;
- fp = skb_clone(head, GFP_ATOMIC);
-
- if (!fp)
- goto out_oom;
-
- fp->next = head->next;
- if (!fp->next)
- fq->q.fragments_tail = fp;
- prev->next = fp;
-
- skb_morph(head, fq->q.fragments);
- head->next = fq->q.fragments->next;
-
- consume_skb(fq->q.fragments);
- fq->q.fragments = head;
- }
-
- WARN_ON(head == NULL);
- WARN_ON(FRAG6_CB(head)->offset != 0);
+ reasm_data = inet_frag_reasm_prepare(&fq->q, skb, prev_tail);
+ if (!reasm_data)
+ goto out_oom;

- /* 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)
goto out_oversize;

- delta = - head->truesize;
-
- /* Head of list must not be cloned. */
- if (skb_unclone(head, GFP_ATOMIC))
- goto out_oom;
-
- 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)
- goto out_oom;
- 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);
- }
-
/* We have to remove fragment header from datagram and to relocate
* header in order to calculate ICV correctly. */
nhoff = fq->nhoffset;
- skb_network_header(head)[nhoff] = skb_transport_header(head)[0];
- memmove(head->head + sizeof(struct frag_hdr), head->head,
- (head->data - head->head) - sizeof(struct frag_hdr));
- if (skb_mac_header_was_set(head))
- head->mac_header += sizeof(struct frag_hdr);
- head->network_header += sizeof(struct frag_hdr);
-
- skb_reset_transport_header(head);
- skb_push(head, head->data - skb_network_header(head));
-
- sum_truesize = head->truesize;
- for (fp = head->next; fp;) {
- bool headstolen;
- int delta;
- struct sk_buff *next = fp->next;
-
- sum_truesize += fp->truesize;
- 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);
-
- if (skb_try_coalesce(head, fp, &headstolen, &delta)) {
- kfree_skb_partial(fp, headstolen);
- } else {
- if (!skb_shinfo(head)->frag_list)
- skb_shinfo(head)->frag_list = fp;
- head->data_len += fp->len;
- head->len += fp->len;
- head->truesize += fp->truesize;
- }
- fp = next;
- }
- sub_frag_mem_limit(fq->q.net, sum_truesize);
+ skb_network_header(skb)[nhoff] = skb_transport_header(skb)[0];
+ memmove(skb->head + sizeof(struct frag_hdr), skb->head,
+ (skb->data - skb->head) - sizeof(struct frag_hdr));
+ if (skb_mac_header_was_set(skb))
+ 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->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)->nhoff = nhoff;
- IP6CB(head)->flags |= IP6SKB_FRAGMENTED;
- IP6CB(head)->frag_max_size = fq->q.max_size;
+ skb->dev = dev;
+ ipv6_hdr(skb)->payload_len = htons(payload_len);
+ ipv6_change_dsfield(ipv6_hdr(skb), 0xff, ecn);
+ IP6CB(skb)->nhoff = nhoff;
+ IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;
+ IP6CB(skb)->frag_max_size = fq->q.max_size;

/* Yes, and fold redundant checksum back. 8) */
- skb_postpush_rcsum(head, skb_network_header(head),
- skb_network_header_len(head));
+ skb_postpush_rcsum(skb, skb_network_header(skb),
+ skb_network_header_len(skb));

rcu_read_lock();
__IP6_INC_STATS(net, __in6_dev_get(dev), IPSTATS_MIB_REASMOKS);
@@ -419,6 +307,7 @@ static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
fq->q.fragments = NULL;
fq->q.rb_fragments = RB_ROOT;
fq->q.fragments_tail = NULL;
+ fq->q.last_run_head = NULL;
return 1;

out_oversize:
@@ -430,6 +319,7 @@ out_fail:
rcu_read_lock();
__IP6_INC_STATS(net, __in6_dev_get(dev), IPSTATS_MIB_REASMFAILS);
rcu_read_unlock();
+ inet_frag_kill(&fq->q);
return -1;
}

@@ -468,10 +358,6 @@ static int ipv6_frag_rcv(struct sk_buff *skb)
return 1;
}

- if (skb->len - skb_network_offset(skb) < IPV6_MIN_MTU &&
- fhdr->frag_off & htons(IP6_MF))
- goto fail_hdr;
-
iif = skb->dev ? skb->dev->ifindex : 0;
fq = fq_find(net, fhdr->identification, hdr, iif);
if (fq) {
@@ -489,6 +375,7 @@ static int ipv6_frag_rcv(struct sk_buff *skb)
if (prob_offset) {
__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
IPSTATS_MIB_INHDRERRORS);
+ /* icmpv6_param_prob() calls kfree_skb(skb) */
icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, prob_offset);
}
return ret;
--
2.19.1