/* * 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 1.58.2.1 2002/01/12 07:53:15 davem Exp $ * * Authors: Fred N. van Kempen * Alan Cox * * 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. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* 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 */ 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 rwlock_t ipfrag_lock = RW_LOCK_UNLOCKED; 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; ip_frag_nqueues--; } static __inline__ void ipq_unlink(struct ipq *ipq) { write_lock(&ipfrag_lock); __ipq_unlink(ipq); write_unlock(&ipfrag_lock); } /* * Was: ((((id) >> 1) ^ (saddr) ^ (daddr) ^ (prot)) & (IPQ_HASHSZ - 1)) * * I see, I see evil hand of bigendian mafia. On Intel all the packets hit * one hash bucket with this hash function. 8) */ static __inline__ unsigned int ipqhashfn(u16 id, u32 saddr, u32 daddr, u8 prot) { unsigned int h = saddr ^ daddr; h ^= (h>>16)^id; h ^= (h>>8)^prot; return h & (IPQ_HASHSZ - 1); } 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) { atomic_sub(skb->truesize, &ip_frag_mem); kfree_skb(skb); } static __inline__ void frag_free_queue(struct ipq *qp) { 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) { 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); fp = xp; } /* Finally, release the queue descriptor itself. */ frag_free_queue(qp); } static __inline__ void ipq_put(struct ipq *ipq) { if (atomic_dec_and_test(&ipq->refcnt)) ip_frag_destroy(ipq); } /* Kill ipq entry. It is not destroyed immediately, * because caller (and someone more) holds reference count. */ static __inline__ 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 low threshold. */ static void ip_evictor(void) { int i, progress; do { if (atomic_read(&ip_frag_mem) <= sysctl_ipfrag_low_thresh) return; progress = 0; /* FIXME: Make LRU queue of frag heads. -DaveM */ for (i = 0; i < IPQ_HASHSZ; i++) { struct ipq *qp; if (ipq_hash[i] == NULL) continue; read_lock(&ipfrag_lock); if ((qp = ipq_hash[i]) != NULL) { /* find the oldest queue for this hash bucket */ while (qp->next) qp = qp->next; 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); IP_INC_STATS_BH(IpReasmFails); progress = 1; continue; } read_unlock(&ipfrag_lock); } } while (progress); } /* * 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(IpReasmTimeout); IP_INC_STATS_BH(IpReasmFails); 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); } /* 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) { atomic_inc(&qp->refcnt); write_unlock(&ipfrag_lock); qp_in->last_in |= COMPLETE; ipq_put(qp_in); 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]; 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) { 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->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 */ qp->lock = SPIN_LOCK_UNLOCKED; atomic_set(&qp->refcnt, 1); return ip_frag_intern(hash, qp); out_nomem: NETDEBUG(if (net_ratelimit()) printk(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) { __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) { atomic_inc(&qp->refcnt); read_unlock(&ipfrag_lock); return qp; } } read_unlock(&ipfrag_lock); return ip_frag_create(hash, iph); } /* 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(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); } } 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; qp->stamp = skb->stamp; qp->meat += skb->len; atomic_add(skb->truesize, &ip_frag_mem); if (offset == 0) qp->last_in |= FIRST_IN; 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; inr_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; head->stamp = qp->stamp; iph = head->nh.iph; iph->frag_off = 0; iph->tot_len = htons(len); IP_INC_STATS_BH(IpReasmOKs); qp->fragments = NULL; return head; out_nomem: NETDEBUG(if (net_ratelimit()) printk(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(IpReasmFails); return NULL; } /* Process an incoming IP datagram fragment. */ struct sk_buff *ip_defrag(struct sk_buff *skb) { struct iphdr *iph = skb->nh.iph; struct ipq *qp; struct net_device *dev; IP_INC_STATS_BH(IpReasmReqds); /* 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)) != 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); return ret; } IP_INC_STATS_BH(IpReasmFails); kfree_skb(skb); return NULL; }