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Date: Thu, 20 Oct 2011 14:39:45 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Alexander Smirnov <alex.bluesman.smirnov@...il.com>
Cc: davem@...emloft.net, dbaryshkov@...il.com, slapin@...fans.org,
linux-zigbee-devel@...ts.sourceforge.net, netdev@...r.kernel.org,
jonsmirl@...il.com
Subject: Re: [IEEE802.15.4][6LoWPAN] draft for fragmentation support
Le jeudi 20 octobre 2011 à 15:17 +0400, Alexander Smirnov a écrit :
> Hello everybody,
>
> below is the patch which adds support for fragmentation in 6LoWPAN
> point to point networks. This activity needs because of difference
> in MTU: 1280 ipv6 and 128 ieee802.15.4
>
> This patch is just a draft. Could anyone please look at
> it and let me know your opinion.
>
I removed janitor list, since this patch is certainly not a janitor one.
> The most doubtful moments for me are:
> 1. Should the list 'frag_list' and the mutex 'flist_lock' be
> included into dev private data?
The mutex is wrong, you need a spinlock since run from softirq handler.
Allocations should use GFP_ATOMIC for same reason.
> 2. Can I use 'dev_queue_xmit' to send fragments to queue?
Well, it is not very clean, but it seems there is no alternative
> 3. Creating new 'skb' instead of copying and modifying main one.
You cant do that without making sure you own the skb and its data.
Think about a sniffer running...
4) No limitation on number of in-flight fragments.
You can consume lot of ram and have a list with 65536 elements...
> net/ieee802154/6lowpan.c | 286
> +++++++++++++++++++++++++++++++++++++++++++++-
> net/ieee802154/6lowpan.h | 3 +
> 2 files changed, 288 insertions(+), 1 deletions(-)
>
> diff --git a/net/ieee802154/6lowpan.c b/net/ieee802154/6lowpan.c
> index 96877bd..1923ec7 100644
> --- a/net/ieee802154/6lowpan.c
> +++ b/net/ieee802154/6lowpan.c
> @@ -113,6 +113,24 @@ struct lowpan_dev_record {
> struct list_head list;
> };
>
> +struct lowpan_fragment {
> + u8 in_progress; /* assembling is in progress
> */
> + struct sk_buff *skb; /* skb to be assembled */
> + u8 *data; /* data to be stored */
> + struct mutex lock; /* concurency lock */
> + u16 length; /* frame length to be assemled
> */
> + u32 bytes_rcv; /* bytes received */
> + u16 tag; /* current fragment tag */
> + struct timer_list timer; /* assembling timer */
> + struct list_head list; /* fragments list handler
> */
> +};
> +
> +static unsigned short fragment_tag;
> +
> +/* TODO: bind mutex and list to device */
> +static LIST_HEAD(lowpan_fragments);
> +struct mutex flist_lock;
> +
> static inline struct
> lowpan_dev_info *lowpan_dev_info(const struct net_device *dev)
> {
> @@ -244,6 +262,18 @@ static u8 lowpan_fetch_skb_u8(struct sk_buff
> *skb)
> return ret;
> }
>
> +static u16 lowpan_fetch_skb_u16(struct sk_buff *skb)
> +{
> + u16 ret;
> +
> + BUG_ON(skb->len < 2);
>
Hmm, check pskb_may_pull(skb, 2), or in caller.
skb->len >= 2 doesnt mean you can access to skb->data[0] and
skb->data[1] : Data might be on a fragment, not on skb head.
> +
> + ret = skb->data[0] | (skb->data[1] << 8);
> + skb_pull(skb, 2);
> + return ret;
> +}
> +
> +static netdev_tx_t lowpan_xmit(struct sk_buff *skb, struct net_device
> *dev);
> static int lowpan_header_create(struct sk_buff *skb,
> struct net_device *dev,
> unsigned short type, const void *_daddr,
> @@ -467,9 +497,102 @@ static int lowpan_header_create(struct sk_buff
> *skb,
> memcpy(&(sa.hwaddr), saddr, 8);
>
> mac_cb(skb)->flags = IEEE802154_FC_TYPE_DATA;
> +
> + /* frame fragmentation */
> +
> + /*
> + * if payload + mac header doesn't fit MTU-sized frame
> + * we need to fragment it.
> + */
> + if (skb->len > (127 - 24)) { /* MTU -
> MAC_HEADER_LENGTH */
> + struct sk_buff *fr_skb;
> + u16 b_sent = 0;
> + unsigned short payload_len = skb->len;
> + int stat = 0;
> +
> + pr_debug("%s: the frame is too big (0x%x),"
> + "fragmentation needed, using tag = 0x
> %x\n",
> + __func__, payload_len, fragment_tag);
> +
> + fr_skb = skb_copy(skb, GFP_KERNEL);
>
GFP_ATOMIC
>
And I wonder why you skb_copy(). You are not allowed to change skb like
that. ( when you later skb_push(fr_skb, 4), you are modifying this skb
data too...)
>
> + if (!fr_skb)
> + goto error;
> +
> + /* 40-bit - fragment dispatch size */
> + head = kzalloc(5, GFP_KERNEL);
GFP_ATOMIC
> + if (!head)
> + goto error;
> +
> + /* first fagment header */
> + head[0] = LOWPAN_DISPATCH_FRAG1 | (payload_len
> & 0x7);
> + head[1] = (payload_len >> 3) & 0xff;
> + head[2] = fragment_tag & 0xff;
> + head[3] = fragment_tag >> 8;
> +
> +
> + lowpan_raw_dump_inline(__func__, "first
> header",
> + head, 4);
> +
> + memcpy(skb_push(fr_skb, 4), head, 4);
> + skb_trim(fr_skb, LOWPAN_FRAG_SIZE);
> +
> + dev_hard_header(fr_skb,
> lowpan_dev_info(dev)->real_dev,
> + type, (void *)&da, (void *)&sa,
> fr_skb->len);
> +
> + /* send fragment to dev queue */
> + dev_queue_xmit(fr_skb);
> +
> + /* next fragments headers */
> + head[0] |= 0x20;
> +
> + lowpan_raw_dump_inline(__func__, "next
> headers",
> + head, 5);
> +
> + while (b_sent < payload_len) {
> + /* not the first fragment */
> + if (b_sent)
> + skb_pull(skb,
> LOWPAN_FRAG_SIZE);
> +
> + pr_debug("%s: preparing fragment %d
> \n",
> + __func__, b_sent /
> LOWPAN_FRAG_SIZE);
> +
> + /*
> + * create copy of current buffer and
> trim it
> + * down to fragment size
> + */
> + fr_skb = skb_copy(skb, GFP_KERNEL);
> + if (!fr_skb)
> + goto error;
> +
> + skb_trim(fr_skb, LOWPAN_FRAG_SIZE);
> +
> + /* add fragment header */
> + head[4] = b_sent / 8;
> + memcpy(skb_push(fr_skb, 5), head, 5);
> +
> + b_sent += LOWPAN_FRAG_SIZE;
> +
> + lowpan_raw_dump_table(__func__,
> + "fragment data", fr_skb->data,
> fr_skb->len);
> +
> + stat = dev_hard_header(fr_skb,
> + lowpan_dev_info(dev)->real_dev, type,
> + (void *)&da, (void *)&sa,
> fr_skb->len);
> +
> + dev_queue_xmit(fr_skb);
> + }
> +
> + /* TODO: what's the correct way to skip
> default skb? */
> +
> + fragment_tag++;
> + return stat;
> + } else
> return dev_hard_header(skb,
> lowpan_dev_info(dev)->real_dev,
> type, (void *)&da, (void *)&sa,
> skb->len);
> }
> +error:
> + kfree_skb(skb);
> + return -ENOMEM;
> }
>
> static int lowpan_skb_deliver(struct sk_buff *skb, struct ipv6hdr
> *hdr)
> @@ -511,6 +634,23 @@ static int lowpan_skb_deliver(struct sk_buff
> *skb, struct ipv6hdr *hdr)
> return stat;
> }
>
> +static void lowpan_fragment_timer_expired(unsigned long tag)
> +{
> + struct lowpan_fragment *entry, *tmp;
> +
> + pr_debug("%s: timer expired for frame with tag %lu\n",
> __func__, tag);
> +
> + mutex_lock(&flist_lock);
>
>
A mutex_lock() is not allowed in this context (softirq).
You must use a spinlock.
>
>
> + list_for_each_entry_safe(entry, tmp, &lowpan_fragments, list)
> + if (entry->tag == tag) {
>
>
Since you have a timer per entry, instead of doing a lookup to find
'tag', you could just say 'tag' is the pointer to your "struct
lowpan_fragment"
>
> + list_del(&entry->list);
> + kfree(entry->data);
> + kfree(entry);
> + break;
> + }
> + mutex_unlock(&flist_lock);
> +}
>
struct lowpan_fragment *entry = (struct lowpan_fragment *)tag;
spin_lock();
list_del(&entry->list);
kfree(entry->data);
kfree(entry);
spin_unlock();
>
> +
> static int
> lowpan_process_data(struct sk_buff *skb)
> {
> @@ -525,6 +665,139 @@ lowpan_process_data(struct sk_buff *skb)
> if (skb->len < 2)
> goto drop;
> iphc0 = lowpan_fetch_skb_u8(skb);
> +
> + /* fragments assmebling */
> + switch (iphc0 & 0xf8) {
0xf8 means ? Please use a macro or something...
>
> + /* first fragment of the frame */
> + case LOWPAN_DISPATCH_FRAG1:
> + {
> + struct lowpan_fragment *entry, *frame;
> + u16 tag;
> +
> + lowpan_raw_dump_inline(__func__, "first frame fragment
> header",
> + skb->data, 3);
> +
> + tmp = lowpan_fetch_skb_u8(skb);
> + tag = lowpan_fetch_skb_u16(skb);
> +
> + /*
> + * check if frame assembling with the same tag is
> + * already in progress
> + */
> + rcu_read_lock();
> + list_for_each_entry_rcu(entry, &lowpan_fragments,
> list)
> + if (entry->tag == tag) {
> + pr_debug("%s ERROR: frame with this
> tag is"
> + "alredy in assembling",
> __func__);
> + goto drop_rcu;
> + }
> + rcu_read_unlock();
> +
> + /* alloc new frame structure */
> + frame = kzalloc(sizeof(struct lowpan_fragment),
> GFP_KERNEL);
>
>
GFP_ATOMIC
>
> + if (!frame)
> + goto drop;
> +
> + INIT_LIST_HEAD(&frame->list);
> +
> + frame->bytes_rcv = 0;
> + frame->length = (iphc0 & 7) | (tmp << 3);
> + frame->tag = tag;
> + /* allocate buffer for frame assembling */
> + frame->data = kzalloc(frame->length, GFP_KERNEL);
>
>
GFP_ATOMIC
> + if (!frame->data) {
> + kfree(frame);
> + goto drop;
> + }
> +
> + pr_debug("%s: frame to be assembled: length = 0x%x, "
> + "tag = 0x%x\n", __func__, frame->length,
> frame->tag);
> +
> + init_timer(&frame->timer);
> + /* (number of fragments) * (fragment processing
> time-out) */
> + frame->timer.expires = jiffies +
> + (frame->length / LOWPAN_FRAG_SIZE + 1) *
> LOWPAN_FRAG_TIMEOUT;
> + frame->timer.data = tag;
> + frame->timer.function = lowpan_fragment_timer_expired;
> +
> + add_timer(&frame->timer);
> +
> + mutex_lock(&flist_lock);
> + list_add_tail(&frame->list, &lowpan_fragments);
> + mutex_unlock(&flist_lock);
> +
> + return kfree_skb(skb), 0;
> + }
> + /* second and next fragment of the frame */
> + case LOWPAN_DISPATCH_FRAGN:
> + {
> + u16 tag;
> + struct lowpan_fragment *entry, *t;
> +
> + lowpan_raw_dump_inline(__func__, "next fragment
> header",
> + skb->data, 4);
> +
> + lowpan_fetch_skb_u8(skb); /* skip frame length byte */
> + tag = lowpan_fetch_skb_u16(skb);
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(entry, &lowpan_fragments,
> list)
> + if (entry->tag == tag)
> + break;
> + rcu_read_unlock();
> +
> + if (entry->tag != tag) {
> + pr_debug("%s ERROR: no frame structure found
> for this"
> + "fragment", __func__);
> + goto drop;
> + }
> +
> + tmp = lowpan_fetch_skb_u8(skb); /* fetch offset */
> +
> + lowpan_raw_dump_table(__func__, "next fragment
> payload",
> + skb->data, skb->len);
> +
> + /* if payload fits buffer, copy it */
> + if ((tmp * 8 + skb->len) <= entry->length) /* TODO:
> likely? */
> + memcpy(entry->data + tmp * 8, skb->data,
> skb->len);
> + else
> + goto drop;
> +
> + entry->bytes_rcv += skb->len;
> +
> + pr_debug("%s: frame length = 0x%x, bytes received = 0x
> %x\n",
> + __func__, entry->length, entry->bytes_rcv);
> +
> + /* frame assembling complete */
> + if (entry->bytes_rcv == entry->length) {
> + struct sk_buff *tmp = skb;
> +
> + mutex_lock(&flist_lock);
> + list_for_each_entry_safe(entry, t,
> &lowpan_fragments, list)
> + if (entry->tag == tag) {
> + list_del(&entry->list);
> + /* copy and clear skb */
> + skb = skb_copy_expand(skb,
> entry->length, skb_tailroom(skb), GFP_KERNEL);
> + skb_pull(skb, skb->len);
> + /* copy new data to skb */
> + memcpy(skb_push(skb,
> entry->length), entry->data, entry->length);
> + kfree_skb(tmp);
> + del_timer(&entry->timer);
> + kfree(entry->data);
> + kfree(entry);
> +
> + iphc0 =
> lowpan_fetch_skb_u8(skb);
> + break;
> + }
> + mutex_unlock(&flist_lock);
> + break;
> + }
> + return kfree_skb(skb), 0;
> + }
> + default:
> + break;
> + }
> +
> iphc1 = lowpan_fetch_skb_u8(skb);
>
> _saddr = mac_cb(skb)->sa.hwaddr;
> @@ -674,6 +947,8 @@ lowpan_process_data(struct sk_buff *skb)
> lowpan_raw_dump_table(__func__, "raw header dump", (u8 *)&hdr,
> sizeof(hdr));
> return lowpan_skb_deliver(skb, &hdr);
> +drop_rcu:
> + rcu_read_unlock();
> drop:
> kfree(skb);
> return -EINVAL;
> @@ -765,8 +1040,15 @@ static int lowpan_rcv(struct sk_buff *skb,
> struct net_device *dev,
> goto drop;
>
> /* check that it's our buffer */
> - if ((skb->data[0] & 0xe0) == 0x60)
> + switch (skb->data[0] & 0xe0) {
> + case 0x60: /* ipv6 datagram */
> + case 0xc0: /* first fragment header */
> + case 0xe0: /* next fragments headers */
> lowpan_process_data(skb);
> + break;
> + default:
> + break;
> + }
>
> return NET_RX_SUCCESS;
>
> @@ -793,6 +1075,8 @@ static int lowpan_newlink(struct net *src_net,
> struct net_device *dev,
> lowpan_dev_info(dev)->real_dev = real_dev;
> mutex_init(&lowpan_dev_info(dev)->dev_list_mtx);
>
> + mutex_init(&flist_lock);
>
>
Doing this init each time a link is setup is wrong.
Do it once.
>
> +
> entry = kzalloc(sizeof(struct lowpan_dev_record), GFP_KERNEL);
> if (!entry)
> return -ENOMEM;
> diff --git a/net/ieee802154/6lowpan.h b/net/ieee802154/6lowpan.h
> index 5d8cf80..e8e57c4 100644
> --- a/net/ieee802154/6lowpan.h
> +++ b/net/ieee802154/6lowpan.h
> @@ -159,6 +159,9 @@
> #define LOWPAN_DISPATCH_FRAG1 0xc0 /* 11000xxx */
> #define LOWPAN_DISPATCH_FRAGN 0xe0 /* 11100xxx */
>
> +#define LOWPAN_FRAG_SIZE 40 /* fragment payload
> size */
> +#define LOWPAN_FRAG_TIMEOUT (HZ * 2) /* processing time: 2
> sec */
> +
> /*
> * Values of fields within the IPHC encoding first byte
> * (C stands for compressed and I for inline)
> --
> 1.7.2.5
>
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