text: /*
   * Linux Socket Filter - Kernel level socket filtering
   *
   * Author:
   *     Jay Schulist <jschlst@samba.org>
   *
   * Based on the design of:
   *     - The Berkeley Packet Filter
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   *
   * Andi Kleen - Fix a few bad bugs and races.
   * Kris Katterjohn - Added many additional checks in sk_chk_filter()
   */
  
  #include <linux/module.h>
  #include <linux/types.h>
  #include <linux/mm.h>
  #include <linux/fcntl.h>
  #include <linux/socket.h>
  #include <linux/in.h>
  #include <linux/inet.h>
  #include <linux/netdevice.h>
  #include <linux/if_packet.h>
  #include <net/ip.h>
  #include <net/protocol.h>
  #include <net/netlink.h>
  #include <linux/skbuff.h>
  #include <net/sock.h>
  #include <linux/errno.h>
  #include <linux/timer.h>
  #include <asm/system.h>
  #include <asm/uaccess.h>
  #include <asm/unaligned.h>
  #include <linux/filter.h>
  
  /* No hurry in this branch */
  static void *__load_pointer(struct sk_buff *skb, int k)
  {
  	u8 *ptr = NULL;
  
  	if (k >= SKF_NET_OFF)
  		ptr = skb_network_header(skb) + k - SKF_NET_OFF;
  	else if (k >= SKF_LL_OFF)
  		ptr = skb_mac_header(skb) + k - SKF_LL_OFF;
  
  	if (ptr >= skb->head && ptr < skb_tail_pointer(skb))
  		return ptr;
  	return NULL;
  }
  
  static inline void *load_pointer(struct sk_buff *skb, int k,
  				 unsigned int size, void *buffer)
  {
  	if (k >= 0)
  		return skb_header_pointer(skb, k, size, buffer);
  	else {
  		if (k >= SKF_AD_OFF)
  			return NULL;
  		return __load_pointer(skb, k);
  	}
  }
  
  /**
   *	sk_filter - run a packet through a socket filter
   *	@sk: sock associated with &sk_buff
   *	@skb: buffer to filter
   *
   * Run the filter code and then cut skb->data to correct size returned by
   * sk_run_filter. If pkt_len is 0 we toss packet. If skb->len is smaller
   * than pkt_len we keep whole skb->data. This is the socket level
   * wrapper to sk_run_filter. It returns 0 if the packet should
   * be accepted or -EPERM if the packet should be tossed.
   *
   */
  int sk_filter(struct sock *sk, struct sk_buff *skb)
  {
  	int err;
  	struct sk_filter *filter;
  
  	err = security_sock_rcv_skb(sk, skb);
  	if (err)
  		return err;
  
  	rcu_read_lock_bh();
  	filter = rcu_dereference(sk->sk_filter);
  	if (filter) {
  		unsigned int pkt_len = sk_run_filter(skb, filter->insns,
  				filter->len);
  		err = pkt_len ? pskb_trim(skb, pkt_len) : -EPERM;
  	}
  	rcu_read_unlock_bh();
  
  	return err;
  }
  EXPORT_SYMBOL(sk_filter);
  
  /**
   *	sk_run_filter - run a filter on a socket
   *	@skb: buffer to run the filter on
   *	@filter: filter to apply
   *	@flen: length of filter
   *
   * Decode and apply filter instructions to the skb->data.
   * Return length to keep, 0 for none. skb is the data we are
   * filtering, filter is the array of filter instructions, and
   * len is the number of filter blocks in the array.
   */
  unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int flen)
  {
  	struct sock_filter *fentry;	/* We walk down these */
  	void *ptr;
  	u32 A = 0;			/* Accumulator */
  	u32 X = 0;			/* Index Register */
  	u32 mem[BPF_MEMWORDS];		/* Scratch Memory Store */
  	u32 tmp;
  	int k;
  	int pc;
  
  	/*
  	 * Process array of filter instructions.
  	 */
  	for (pc = 0; pc < flen; pc++) {
  		fentry = &filter[pc];
  
  		switch (fentry->code) {
  		case BPF_ALU|BPF_ADD|BPF_X:
  			A += X;
  			continue;
  		case BPF_ALU|BPF_ADD|BPF_K:
  			A += fentry->k;
  			continue;
  		case BPF_ALU|BPF_SUB|BPF_X:
  			A -= X;
  			continue;
  		case BPF_ALU|BPF_SUB|BPF_K:
  			A -= fentry->k;
  			continue;
  		case BPF_ALU|BPF_MUL|BPF_X:
  			A *= X;
  			continue;
  		case BPF_ALU|BPF_MUL|BPF_K:
  			A *= fentry->k;
  			continue;
  		case BPF_ALU|BPF_DIV|BPF_X:
  			if (X == 0)
  				return 0;
  			A /= X;
  			continue;
  		case BPF_ALU|BPF_DIV|BPF_K:
  			A /= fentry->k;
  			continue;
  		case BPF_ALU|BPF_AND|BPF_X:
  			A &= X;
  			continue;
  		case BPF_ALU|BPF_AND|BPF_K:
  			A &= fentry->k;
  			continue;
  		case BPF_ALU|BPF_OR|BPF_X:
  			A |= X;
  			continue;
  		case BPF_ALU|BPF_OR|BPF_K:
  			A |= fentry->k;
  			continue;
  		case BPF_ALU|BPF_LSH|BPF_X:
  			A <<= X;
  			continue;
  		case BPF_ALU|BPF_LSH|BPF_K:
  			A <<= fentry->k;
  			continue;
  		case BPF_ALU|BPF_RSH|BPF_X:
  			A >>= X;
  			continue;
  		case BPF_ALU|BPF_RSH|BPF_K:
  			A >>= fentry->k;
  			continue;
  		case BPF_ALU|BPF_NEG:
  			A = -A;
  			continue;
  		case BPF_JMP|BPF_JA:
  			pc += fentry->k;
  			continue;
  		case BPF_JMP|BPF_JGT|BPF_K:
  			pc += (A > fentry->k) ? fentry->jt : fentry->jf;
  			continue;
  		case BPF_JMP|BPF_JGE|BPF_K:
  			pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
  			continue;
  		case BPF_JMP|BPF_JEQ|BPF_K:
  			pc += (A == fentry->k) ? fentry->jt : fentry->jf;
  			continue;
  		case BPF_JMP|BPF_JSET|BPF_K:
  			pc += (A & fentry->k) ? fentry->jt : fentry->jf;
  			continue;
  		case BPF_JMP|BPF_JGT|BPF_X:
  			pc += (A > X) ? fentry->jt : fentry->jf;
  			continue;
  		case BPF_JMP|BPF_JGE|BPF_X:
  			pc += (A >= X) ? fentry->jt : fentry->jf;
  			continue;
  		case BPF_JMP|BPF_JEQ|BPF_X:
  			pc += (A == X) ? fentry->jt : fentry->jf;
  			continue;
  		case BPF_JMP|BPF_JSET|BPF_X:
  			pc += (A & X) ? fentry->jt : fentry->jf;
  			continue;
  		case BPF_LD|BPF_W|BPF_ABS:
  			k = fentry->k;
  load_w:
  			ptr = load_pointer(skb, k, 4, &tmp);
  			if (ptr != NULL) {
  				A = get_unaligned_be32(ptr);
  				continue;
  			}
  			break;
  		case BPF_LD|BPF_H|BPF_ABS:
  			k = fentry->k;
  load_h:
  			ptr = load_pointer(skb, k, 2, &tmp);
  			if (ptr != NULL) {
  				A = get_unaligned_be16(ptr);
  				continue;
  			}
  			break;
  		case BPF_LD|BPF_B|BPF_ABS:
  			k = fentry->k;
  load_b:
  			ptr = load_pointer(skb, k, 1, &tmp);
  			if (ptr != NULL) {
  				A = *(u8 *)ptr;
  				continue;
  			}
  			break;
  		case BPF_LD|BPF_W|BPF_LEN:
  			A = skb->len;
  			continue;
  		case BPF_LDX|BPF_W|BPF_LEN:
  			X = skb->len;
  			continue;
  		case BPF_LD|BPF_W|BPF_IND:
  			k = X + fentry->k;
  			goto load_w;
  		case BPF_LD|BPF_H|BPF_IND:
  			k = X + fentry->k;
  			goto load_h;
  		case BPF_LD|BPF_B|BPF_IND:
  			k = X + fentry->k;
  			goto load_b;
  		case BPF_LDX|BPF_B|BPF_MSH:
  			ptr = load_pointer(skb, fentry->k, 1, &tmp);
  			if (ptr != NULL) {
  				X = (*(u8 *)ptr & 0xf) << 2;
  				continue;
  			}
  			return 0;
  		case BPF_LD|BPF_IMM:
  			A = fentry->k;
  			continue;
  		case BPF_LDX|BPF_IMM:
  			X = fentry->k;
  			continue;
  		case BPF_LD|BPF_MEM:
  			A = mem[fentry->k];
  			continue;
  		case BPF_LDX|BPF_MEM:
  			X = mem[fentry->k];
  			continue;
  		case BPF_MISC|BPF_TAX:
  			X = A;
  			continue;
  		case BPF_MISC|BPF_TXA:
  			A = X;
  			continue;
  		case BPF_RET|BPF_K:
  			return fentry->k;
  		case BPF_RET|BPF_A:
  			return A;
  		case BPF_ST:
  			mem[fentry->k] = A;
  			continue;
  		case BPF_STX:
  			mem[fentry->k] = X;
  			continue;
  		default:
  			WARN_ON(1);
  			return 0;
  		}
  
  		/*
  		 * Handle ancillary data, which are impossible
  		 * (or very difficult) to get parsing packet contents.
  		 */
  		switch (k-SKF_AD_OFF) {
  		case SKF_AD_PROTOCOL:
  			A = ntohs(skb->protocol);
  			continue;
  		case SKF_AD_PKTTYPE:
  			A = skb->pkt_type;
  			continue;
  		case SKF_AD_IFINDEX:
  			A = skb->dev->ifindex;
  			continue;
  		case SKF_AD_NLATTR: {
  			struct nlattr *nla;
  
  			if (skb_is_nonlinear(skb))
  				return 0;
  			if (A > skb->len - sizeof(struct nlattr))
  				return 0;
  
  			nla = nla_find((struct nlattr *)&skb->data[A],
  				       skb->len - A, X);
  			if (nla)
  				A = (void *)nla - (void *)skb->data;
  			else
  				A = 0;
  			continue;
  		}
  		case SKF_AD_NLATTR_NEST: {
  			struct nlattr *nla;
  
  			if (skb_is_nonlinear(skb))
  				return 0;
  			if (A > skb->len - sizeof(struct nlattr))
  				return 0;
  
  			nla = (struct nlattr *)&skb->data[A];
  			if (nla->nla_len > A - skb->len)
  				return 0;
  
  			nla = nla_find_nested(nla, X);
  			if (nla)
  				A = (void *)nla - (void *)skb->data;
  			else
  				A = 0;
  			continue;
  		}
  		default:
  			return 0;
  		}
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL(sk_run_filter);
  
  /**
   *	sk_chk_filter - verify socket filter code
   *	@filter: filter to verify
   *	@flen: length of filter
   *
   * Check the user's filter code. If we let some ugly
   * filter code slip through kaboom! The filter must contain
   * no references or jumps that are out of range, no illegal
   * instructions, and must end with a RET instruction.
   *
   * All jumps are forward as they are not signed.
   *
   * Returns 0 if the rule set is legal or -EINVAL if not.
   */
  int sk_chk_filter(struct sock_filter *filter, int flen)
  {
  	struct sock_filter *ftest;
  	int pc;
  
  	if (flen == 0 || flen > BPF_MAXINSNS)
  		return -EINVAL;
  
  	/* check the filter code now */
  	for (pc = 0; pc < flen; pc++) {
  		ftest = &filter[pc];
  
  		/* Only allow valid instructions */
  		switch (ftest->code) {
  		case BPF_ALU|BPF_ADD|BPF_K:
  		case BPF_ALU|BPF_ADD|BPF_X:
  		case BPF_ALU|BPF_SUB|BPF_K:
  		case BPF_ALU|BPF_SUB|BPF_X:
  		case BPF_ALU|BPF_MUL|BPF_K:
  		case BPF_ALU|BPF_MUL|BPF_X:
  		case BPF_ALU|BPF_DIV|BPF_X:
  		case BPF_ALU|BPF_AND|BPF_K:
  		case BPF_ALU|BPF_AND|BPF_X:
  		case BPF_ALU|BPF_OR|BPF_K:
  		case BPF_ALU|BPF_OR|BPF_X:
  		case BPF_ALU|BPF_LSH|BPF_K:
  		case BPF_ALU|BPF_LSH|BPF_X:
  		case BPF_ALU|BPF_RSH|BPF_K:
  		case BPF_ALU|BPF_RSH|BPF_X:
  		case BPF_ALU|BPF_NEG:
  		case BPF_LD|BPF_W|BPF_ABS:
  		case BPF_LD|BPF_H|BPF_ABS:
  		case BPF_LD|BPF_B|BPF_ABS:
  		case BPF_LD|BPF_W|BPF_LEN:
  		case BPF_LD|BPF_W|BPF_IND:
  		case BPF_LD|BPF_H|BPF_IND:
  		case BPF_LD|BPF_B|BPF_IND:
  		case BPF_LD|BPF_IMM:
  		case BPF_LDX|BPF_W|BPF_LEN:
  		case BPF_LDX|BPF_B|BPF_MSH:
  		case BPF_LDX|BPF_IMM:
  		case BPF_MISC|BPF_TAX:
  		case BPF_MISC|BPF_TXA:
  		case BPF_RET|BPF_K:
  		case BPF_RET|BPF_A:
  			break;
  
  		/* Some instructions need special checks */
  
  		case BPF_ALU|BPF_DIV|BPF_K:
  			/* check for division by zero */
  			if (ftest->k == 0)
  				return -EINVAL;
  			break;
  
  		case BPF_LD|BPF_MEM:
  		case BPF_LDX|BPF_MEM:
  		case BPF_ST:
  		case BPF_STX:
  			/* check for invalid memory addresses */
  			if (ftest->k >= BPF_MEMWORDS)
  				return -EINVAL;
  			break;
  
  		case BPF_JMP|BPF_JA:
  			/*
  			 * Note, the large ftest->k might cause loops.
  			 * Compare this with conditional jumps below,
  			 * where offsets are limited. --ANK (981016)
  			 */
  			if (ftest->k >= (unsigned)(flen-pc-1))
  				return -EINVAL;
  			break;
  
  		case BPF_JMP|BPF_JEQ|BPF_K:
  		case BPF_JMP|BPF_JEQ|BPF_X:
  		case BPF_JMP|BPF_JGE|BPF_K:
  		case BPF_JMP|BPF_JGE|BPF_X:
  		case BPF_JMP|BPF_JGT|BPF_K:
  		case BPF_JMP|BPF_JGT|BPF_X:
  		case BPF_JMP|BPF_JSET|BPF_K:
  		case BPF_JMP|BPF_JSET|BPF_X:
  			/* for conditionals both must be safe */
  			if (pc + ftest->jt + 1 >= flen ||
  			    pc + ftest->jf + 1 >= flen)
  				return -EINVAL;
  			break;
  
  		default:
  			return -EINVAL;
  		}
  	}
  
  	return (BPF_CLASS(filter[flen - 1].code) == BPF_RET) ? 0 : -EINVAL;
  }
  EXPORT_SYMBOL(sk_chk_filter);
  
  /**
   * 	sk_filter_rcu_release: Release a socket filter by rcu_head
   *	@rcu: rcu_head that contains the sk_filter to free
   */
  static void sk_filter_rcu_release(struct rcu_head *rcu)
  {
  	struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
  
  	sk_filter_release(fp);
  }
  
  static void sk_filter_delayed_uncharge(struct sock *sk, struct sk_filter *fp)
  {
  	unsigned int size = sk_filter_len(fp);
  
  	atomic_sub(size, &sk->sk_omem_alloc);
  	call_rcu_bh(&fp->rcu, sk_filter_rcu_release);
  }
  
  /**
   *	sk_attach_filter - attach a socket filter
   *	@fprog: the filter program
   *	@sk: the socket to use
   *
   * Attach the user's filter code. We first run some sanity checks on
   * it to make sure it does not explode on us later. If an error
   * occurs or there is insufficient memory for the filter a negative
   * errno code is returned. On success the return is zero.
   */
  int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
  {
  	struct sk_filter *fp, *old_fp;
  	unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
  	int err;
  
  	/* Make sure new filter is there and in the right amounts. */
  	if (fprog->filter == NULL)
  		return -EINVAL;
  
  	fp = sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
  	if (!fp)
  		return -ENOMEM;
  	if (copy_from_user(fp->insns, fprog->filter, fsize)) {
  		sock_kfree_s(sk, fp, fsize+sizeof(*fp));
  		return -EFAULT;
  	}
  
  	atomic_set(&fp->refcnt, 1);
  	fp->len = fprog->len;
  
  	err = sk_chk_filter(fp->insns, fp->len);
  	if (err) {
  		sk_filter_uncharge(sk, fp);
  		return err;
  	}
  
  	rcu_read_lock_bh();
  	old_fp = rcu_dereference(sk->sk_filter);
  	rcu_assign_pointer(sk->sk_filter, fp);
  	rcu_read_unlock_bh();
  
  	if (old_fp)
  		sk_filter_delayed_uncharge(sk, old_fp);
  	return 0;
  }
  
  int sk_detach_filter(struct sock *sk)
  {
  	int ret = -ENOENT;
  	struct sk_filter *filter;
  
  	rcu_read_lock_bh();
  	filter = rcu_dereference(sk->sk_filter);
  	if (filter) {
  		rcu_assign_pointer(sk->sk_filter, NULL);
  		sk_filter_delayed_uncharge(sk, filter);
  		ret = 0;
  	}
  	rcu_read_unlock_bh();
  	return ret;
  }
  