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linux/net/ipv4/ip_fragment.c

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/*
* INET An implementation of the TCP/IP protocol suite for the LINUX
* operating system. INET is implemented using the BSD Socket
* interface as the means of communication with the user level.
*
* The IP fragmentation functionality.
*
* Version: $Id: ip_fragment.c,v 1.59 2002/01/12 07:54:56 davem Exp $
*
* Authors: Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
* Alan Cox <Alan.Cox@linux.org>
*
* Fixes:
* Alan Cox : Split from ip.c , see ip_input.c for history.
* David S. Miller : Begin massive cleanup...
* Andi Kleen : Add sysctls.
* xxxx : Overlapfrag bug.
* Ultima : ip_expire() kernel panic.
* Bill Hawes : Frag accounting and evictor fixes.
* John McDonald : 0 length frag bug.
* Alexey Kuznetsov: SMP races, threading, cleanup.
* Patrick McHardy : LRU queue of frag heads for evictor.
*/
#include <linux/config.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/jiffies.h>
#include <linux/skbuff.h>
#include <linux/list.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <linux/netdevice.h>
#include <linux/jhash.h>
#include <linux/random.h>
#include <net/sock.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/checksum.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/inet.h>
#include <linux/netfilter_ipv4.h>
/* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
* code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
* as well. Or notify me, at least. --ANK
*/
/* Fragment cache limits. We will commit 256K at one time. Should we
* cross that limit we will prune down to 192K. This should cope with
* even the most extreme cases without allowing an attacker to measurably
* harm machine performance.
*/
int sysctl_ipfrag_high_thresh = 256*1024;
int sysctl_ipfrag_low_thresh = 192*1024;
/* Important NOTE! Fragment queue must be destroyed before MSL expires.
* RFC791 is wrong proposing to prolongate timer each fragment arrival by TTL.
*/
int sysctl_ipfrag_time = IP_FRAG_TIME;
struct ipfrag_skb_cb
{
struct inet_skb_parm h;
int offset;
};
#define FRAG_CB(skb) ((struct ipfrag_skb_cb*)((skb)->cb))
/* Describe an entry in the "incomplete datagrams" queue. */
struct ipq {
struct ipq *next; /* linked list pointers */
struct list_head lru_list; /* lru list member */
u32 user;
u32 saddr;
u32 daddr;
u16 id;
u8 protocol;
u8 last_in;
#define COMPLETE 4
#define FIRST_IN 2
#define LAST_IN 1
struct sk_buff *fragments; /* linked list of received fragments */
int len; /* total length of original datagram */
int meat;
spinlock_t lock;
atomic_t refcnt;
struct timer_list timer; /* when will this queue expire? */
struct ipq **pprev;
int iif;
struct timeval stamp;
};
/* Hash table. */
#define IPQ_HASHSZ 64
/* Per-bucket lock is easy to add now. */
static struct ipq *ipq_hash[IPQ_HASHSZ];
static DEFINE_RWLOCK(ipfrag_lock);
static u32 ipfrag_hash_rnd;
static LIST_HEAD(ipq_lru_list);
int ip_frag_nqueues = 0;
static __inline__ void __ipq_unlink(struct ipq *qp)
{
if(qp->next)
qp->next->pprev = qp->pprev;
*qp->pprev = qp->next;
list_del(&qp->lru_list);
ip_frag_nqueues--;
}
static __inline__ void ipq_unlink(struct ipq *ipq)
{
write_lock(&ipfrag_lock);
__ipq_unlink(ipq);
write_unlock(&ipfrag_lock);
}
static unsigned int ipqhashfn(u16 id, u32 saddr, u32 daddr, u8 prot)
{
return jhash_3words((u32)id << 16 | prot, saddr, daddr,
ipfrag_hash_rnd) & (IPQ_HASHSZ - 1);
}
static struct timer_list ipfrag_secret_timer;
int sysctl_ipfrag_secret_interval = 10 * 60 * HZ;
static void ipfrag_secret_rebuild(unsigned long dummy)
{
unsigned long now = jiffies;
int i;
write_lock(&ipfrag_lock);
get_random_bytes(&ipfrag_hash_rnd, sizeof(u32));
for (i = 0; i < IPQ_HASHSZ; i++) {
struct ipq *q;
q = ipq_hash[i];
while (q) {
struct ipq *next = q->next;
unsigned int hval = ipqhashfn(q->id, q->saddr,
q->daddr, q->protocol);
if (hval != i) {
/* Unlink. */
if (q->next)
q->next->pprev = q->pprev;
*q->pprev = q->next;
/* Relink to new hash chain. */
if ((q->next = ipq_hash[hval]) != NULL)
q->next->pprev = &q->next;
ipq_hash[hval] = q;
q->pprev = &ipq_hash[hval];
}
q = next;
}
}
write_unlock(&ipfrag_lock);
mod_timer(&ipfrag_secret_timer, now + sysctl_ipfrag_secret_interval);
}
atomic_t ip_frag_mem = ATOMIC_INIT(0); /* Memory used for fragments */
/* Memory Tracking Functions. */
static __inline__ void frag_kfree_skb(struct sk_buff *skb, int *work)
{
if (work)
*work -= skb->truesize;
atomic_sub(skb->truesize, &ip_frag_mem);
kfree_skb(skb);
}
static __inline__ void frag_free_queue(struct ipq *qp, int *work)
{
if (work)
*work -= sizeof(struct ipq);
atomic_sub(sizeof(struct ipq), &ip_frag_mem);
kfree(qp);
}
static __inline__ struct ipq *frag_alloc_queue(void)
{
struct ipq *qp = kmalloc(sizeof(struct ipq), GFP_ATOMIC);
if(!qp)
return NULL;
atomic_add(sizeof(struct ipq), &ip_frag_mem);
return qp;
}
/* Destruction primitives. */
/* Complete destruction of ipq. */
static void ip_frag_destroy(struct ipq *qp, int *work)
{
struct sk_buff *fp;
BUG_TRAP(qp->last_in&COMPLETE);
BUG_TRAP(del_timer(&qp->timer) == 0);
/* Release all fragment data. */
fp = qp->fragments;
while (fp) {
struct sk_buff *xp = fp->next;
frag_kfree_skb(fp, work);
fp = xp;
}
/* Finally, release the queue descriptor itself. */
frag_free_queue(qp, work);
}
static __inline__ void ipq_put(struct ipq *ipq, int *work)
{
if (atomic_dec_and_test(&ipq->refcnt))
ip_frag_destroy(ipq, work);
}
/* Kill ipq entry. It is not destroyed immediately,
* because caller (and someone more) holds reference count.
*/
static void ipq_kill(struct ipq *ipq)
{
if (del_timer(&ipq->timer))
atomic_dec(&ipq->refcnt);
if (!(ipq->last_in & COMPLETE)) {
ipq_unlink(ipq);
atomic_dec(&ipq->refcnt);
ipq->last_in |= COMPLETE;
}
}
/* Memory limiting on fragments. Evictor trashes the oldest
* fragment queue until we are back under the threshold.
*/
static void ip_evictor(void)
{
struct ipq *qp;
struct list_head *tmp;
int work;
work = atomic_read(&ip_frag_mem) - sysctl_ipfrag_low_thresh;
if (work <= 0)
return;
while (work > 0) {
read_lock(&ipfrag_lock);
if (list_empty(&ipq_lru_list)) {
read_unlock(&ipfrag_lock);
return;
}
tmp = ipq_lru_list.next;
qp = list_entry(tmp, struct ipq, lru_list);
atomic_inc(&qp->refcnt);
read_unlock(&ipfrag_lock);
spin_lock(&qp->lock);
if (!(qp->last_in&COMPLETE))
ipq_kill(qp);
spin_unlock(&qp->lock);
ipq_put(qp, &work);
IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
}
}
/*
* Oops, a fragment queue timed out. Kill it and send an ICMP reply.
*/
static void ip_expire(unsigned long arg)
{
struct ipq *qp = (struct ipq *) arg;
spin_lock(&qp->lock);
if (qp->last_in & COMPLETE)
goto out;
ipq_kill(qp);
IP_INC_STATS_BH(IPSTATS_MIB_REASMTIMEOUT);
IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
if ((qp->last_in&FIRST_IN) && qp->fragments != NULL) {
struct sk_buff *head = qp->fragments;
/* Send an ICMP "Fragment Reassembly Timeout" message. */
if ((head->dev = dev_get_by_index(qp->iif)) != NULL) {
icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
dev_put(head->dev);
}
}
out:
spin_unlock(&qp->lock);
ipq_put(qp, NULL);
}
/* Creation primitives. */
static struct ipq *ip_frag_intern(unsigned int hash, struct ipq *qp_in)
{
struct ipq *qp;
write_lock(&ipfrag_lock);
#ifdef CONFIG_SMP
/* With SMP race we have to recheck hash table, because
* such entry could be created on other cpu, while we
* promoted read lock to write lock.
*/
for(qp = ipq_hash[hash]; qp; qp = qp->next) {
if(qp->id == qp_in->id &&
qp->saddr == qp_in->saddr &&
qp->daddr == qp_in->daddr &&
qp->protocol == qp_in->protocol &&
qp->user == qp_in->user) {
atomic_inc(&qp->refcnt);
write_unlock(&ipfrag_lock);
qp_in->last_in |= COMPLETE;
ipq_put(qp_in, NULL);
return qp;
}
}
#endif
qp = qp_in;
if (!mod_timer(&qp->timer, jiffies + sysctl_ipfrag_time))
atomic_inc(&qp->refcnt);
atomic_inc(&qp->refcnt);
if((qp->next = ipq_hash[hash]) != NULL)
qp->next->pprev = &qp->next;
ipq_hash[hash] = qp;
qp->pprev = &ipq_hash[hash];
INIT_LIST_HEAD(&qp->lru_list);
list_add_tail(&qp->lru_list, &ipq_lru_list);
ip_frag_nqueues++;
write_unlock(&ipfrag_lock);
return qp;
}
/* Add an entry to the 'ipq' queue for a newly received IP datagram. */
static struct ipq *ip_frag_create(unsigned hash, struct iphdr *iph, u32 user)
{
struct ipq *qp;
if ((qp = frag_alloc_queue()) == NULL)
goto out_nomem;
qp->protocol = iph->protocol;
qp->last_in = 0;
qp->id = iph->id;
qp->saddr = iph->saddr;
qp->daddr = iph->daddr;
qp->user = user;
qp->len = 0;
qp->meat = 0;
qp->fragments = NULL;
qp->iif = 0;
/* Initialize a timer for this entry. */
init_timer(&qp->timer);
qp->timer.data = (unsigned long) qp; /* pointer to queue */
qp->timer.function = ip_expire; /* expire function */
spin_lock_init(&qp->lock);
atomic_set(&qp->refcnt, 1);
return ip_frag_intern(hash, qp);
out_nomem:
LIMIT_NETDEBUG(KERN_ERR "ip_frag_create: no memory left !\n");
return NULL;
}
/* Find the correct entry in the "incomplete datagrams" queue for
* this IP datagram, and create new one, if nothing is found.
*/
static inline struct ipq *ip_find(struct iphdr *iph, u32 user)
{
__u16 id = iph->id;
__u32 saddr = iph->saddr;
__u32 daddr = iph->daddr;
__u8 protocol = iph->protocol;
unsigned int hash = ipqhashfn(id, saddr, daddr, protocol);
struct ipq *qp;
read_lock(&ipfrag_lock);
for(qp = ipq_hash[hash]; qp; qp = qp->next) {
if(qp->id == id &&
qp->saddr == saddr &&
qp->daddr == daddr &&
qp->protocol == protocol &&
qp->user == user) {
atomic_inc(&qp->refcnt);
read_unlock(&ipfrag_lock);
return qp;
}
}
read_unlock(&ipfrag_lock);
return ip_frag_create(hash, iph, user);
}
/* Add new segment to existing queue. */
static void ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
{
struct sk_buff *prev, *next;
int flags, offset;
int ihl, end;
if (qp->last_in & COMPLETE)
goto err;
offset = ntohs(skb->nh.iph->frag_off);
flags = offset & ~IP_OFFSET;
offset &= IP_OFFSET;
offset <<= 3; /* offset is in 8-byte chunks */
ihl = skb->nh.iph->ihl * 4;
/* Determine the position of this fragment. */
end = offset + skb->len - ihl;
/* Is this the final fragment? */
if ((flags & IP_MF) == 0) {
/* If we already have some bits beyond end
* or have different end, the segment is corrrupted.
*/
if (end < qp->len ||
((qp->last_in & LAST_IN) && end != qp->len))
goto err;
qp->last_in |= LAST_IN;
qp->len = end;
} else {
if (end&7) {
end &= ~7;
if (skb->ip_summed != CHECKSUM_UNNECESSARY)
skb->ip_summed = CHECKSUM_NONE;
}
if (end > qp->len) {
/* Some bits beyond end -> corruption. */
if (qp->last_in & LAST_IN)
goto err;
qp->len = end;
}
}
if (end == offset)
goto err;
if (pskb_pull(skb, ihl) == NULL)
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 = NULL;
for(next = qp->fragments; next != NULL; next = next->next) {
if (FRAG_CB(next)->offset >= offset)
break; /* bingo! */
prev = next;
}
/* We found where to put this one. Check for overlap with
* preceding fragment, and, if needed, align things so that
* any overlaps are eliminated.
*/
if (prev) {
int i = (FRAG_CB(prev)->offset + prev->len) - offset;
if (i > 0) {
offset += i;
if (end <= offset)
goto err;
if (!pskb_pull(skb, i))
goto err;
if (skb->ip_summed != CHECKSUM_UNNECESSARY)
skb->ip_summed = CHECKSUM_NONE;
}
}
while (next && FRAG_CB(next)->offset < end) {
int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */
if (i < next->len) {
/* Eat head of the next overlapped fragment
* and leave the loop. The next ones cannot overlap.
*/
if (!pskb_pull(next, i))
goto err;
FRAG_CB(next)->offset += i;
qp->meat -= i;
if (next->ip_summed != CHECKSUM_UNNECESSARY)
next->ip_summed = CHECKSUM_NONE;
break;
} else {
struct sk_buff *free_it = next;
/* Old fragmnet is completely overridden with
* new one drop it.
*/
next = next->next;
if (prev)
prev->next = next;
else
qp->fragments = next;
qp->meat -= free_it->len;
frag_kfree_skb(free_it, NULL);
}
}
FRAG_CB(skb)->offset = offset;
/* Insert this fragment in the chain of fragments. */
skb->next = next;
if (prev)
prev->next = skb;
else
qp->fragments = skb;
if (skb->dev)
qp->iif = skb->dev->ifindex;
skb->dev = NULL;
skb_get_timestamp(skb, &qp->stamp);
qp->meat += skb->len;
atomic_add(skb->truesize, &ip_frag_mem);
if (offset == 0)
qp->last_in |= FIRST_IN;
write_lock(&ipfrag_lock);
list_move_tail(&qp->lru_list, &ipq_lru_list);
write_unlock(&ipfrag_lock);
return;
err:
kfree_skb(skb);
}
/* Build a new IP datagram from all its fragments. */
static struct sk_buff *ip_frag_reasm(struct ipq *qp, struct net_device *dev)
{
struct iphdr *iph;
struct sk_buff *fp, *head = qp->fragments;
int len;
int ihlen;
ipq_kill(qp);
BUG_TRAP(head != NULL);
BUG_TRAP(FRAG_CB(head)->offset == 0);
/* Allocate a new buffer for the datagram. */
ihlen = head->nh.iph->ihl*4;
len = ihlen + qp->len;
if(len > 65535)
goto out_oversize;
/* Head of list must not be cloned. */
if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
goto out_nomem;
/* 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_shinfo(head)->frag_list) {
struct sk_buff *clone;
int i, plen = 0;
if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
goto out_nomem;
clone->next = head->next;
head->next = clone;
skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
skb_shinfo(head)->frag_list = NULL;
for (i=0; i<skb_shinfo(head)->nr_frags; i++)
plen += skb_shinfo(head)->frags[i].size;
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;
atomic_add(clone->truesize, &ip_frag_mem);
}
skb_shinfo(head)->frag_list = head->next;
skb_push(head, head->data - head->nh.raw);
atomic_sub(head->truesize, &ip_frag_mem);
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_HW)
head->csum = csum_add(head->csum, fp->csum);
head->truesize += fp->truesize;
atomic_sub(fp->truesize, &ip_frag_mem);
}
head->next = NULL;
head->dev = dev;
skb_set_timestamp(head, &qp->stamp);
iph = head->nh.iph;
iph->frag_off = 0;
iph->tot_len = htons(len);
IP_INC_STATS_BH(IPSTATS_MIB_REASMOKS);
qp->fragments = NULL;
return head;
out_nomem:
LIMIT_NETDEBUG(KERN_ERR "IP: queue_glue: no memory for gluing "
"queue %p\n", qp);
goto out_fail;
out_oversize:
if (net_ratelimit())
printk(KERN_INFO
"Oversized IP packet from %d.%d.%d.%d.\n",
NIPQUAD(qp->saddr));
out_fail:
IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
return NULL;
}
/* Process an incoming IP datagram fragment. */
struct sk_buff *ip_defrag(struct sk_buff *skb, u32 user)
{
struct iphdr *iph = skb->nh.iph;
struct ipq *qp;
struct net_device *dev;
IP_INC_STATS_BH(IPSTATS_MIB_REASMREQDS);
/* Start by cleaning up the memory. */
if (atomic_read(&ip_frag_mem) > sysctl_ipfrag_high_thresh)
ip_evictor();
dev = skb->dev;
/* Lookup (or create) queue header */
if ((qp = ip_find(iph, user)) != NULL) {
struct sk_buff *ret = NULL;
spin_lock(&qp->lock);
ip_frag_queue(qp, skb);
if (qp->last_in == (FIRST_IN|LAST_IN) &&
qp->meat == qp->len)
ret = ip_frag_reasm(qp, dev);
spin_unlock(&qp->lock);
ipq_put(qp, NULL);
return ret;
}
IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
kfree_skb(skb);
return NULL;
}
void ipfrag_init(void)
{
ipfrag_hash_rnd = (u32) ((num_physpages ^ (num_physpages>>7)) ^
(jiffies ^ (jiffies >> 6)));
init_timer(&ipfrag_secret_timer);
ipfrag_secret_timer.function = ipfrag_secret_rebuild;
ipfrag_secret_timer.expires = jiffies + sysctl_ipfrag_secret_interval;
add_timer(&ipfrag_secret_timer);
}
EXPORT_SYMBOL(ip_defrag);
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