- 根目录:
- net
- core
- filter.c
/*
* 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 <linux/gfp.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>
#include <linux/reciprocal_div.h>
#include <linux/ratelimit.h>
/* No hurry in this branch */
static void *__load_pointer(const struct sk_buff *skb, int k, unsigned int size)
{
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 + size <= skb_tail_pointer(skb))
return ptr;
return NULL;
}
static inline void *load_pointer(const struct sk_buff *skb, int k,
unsigned int size, void *buffer)
{
if (k >= 0)
return skb_header_pointer(skb, k, size, buffer);
return __load_pointer(skb, k, size);
}
/**
* 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();
filter = rcu_dereference(sk->sk_filter);
if (filter) {
unsigned int pkt_len = SK_RUN_FILTER(filter, skb);
err = pkt_len ? pskb_trim(skb, pkt_len) : -EPERM;
}
rcu_read_unlock();
return err;
}
EXPORT_SYMBOL(sk_filter);
/**
* sk_run_filter - run a filter on a socket
* @skb: buffer to run the filter on
* @fentry: filter to apply
*
* 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.
* Because all jumps are guaranteed to be before last instruction,
* and last instruction guaranteed to be a RET, we dont need to check
* flen. (We used to pass to this function the length of filter)
*/
unsigned int sk_run_filter(const struct sk_buff *skb,
const struct sock_filter *fentry)
{
void *ptr;
u32 A = 0; /* Accumulator */
u32 X = 0; /* Index Register */
u32 mem[BPF_MEMWORDS]; /* Scratch Memory Store */
u32 tmp;
int k;
/*
* Process array of filter instructions.
*/
for (;; fentry++) {
#if defined(CONFIG_X86_32)
#define K (fentry->k)
#else
const u32 K = fentry->k;
#endif
switch (fentry->code) {
case BPF_S_ALU_ADD_X:
A += X;
continue;
case BPF_S_ALU_ADD_K:
A += K;
continue;
case BPF_S_ALU_SUB_X:
A -= X;
continue;
case BPF_S_ALU_SUB_K:
A -= K;
continue;
case BPF_S_ALU_MUL_X:
A *= X;
continue;
case BPF_S_ALU_MUL_K:
A *= K;
continue;
case BPF_S_ALU_DIV_X:
if (X == 0)
return 0;
A /= X;
continue;
case BPF_S_ALU_DIV_K:
A = reciprocal_divide(A, K);
continue;
case BPF_S_ALU_AND_X:
A &= X;
continue;
case BPF_S_ALU_AND_K:
A &= K;
continue;
case BPF_S_ALU_OR_X:
A |= X;
continue;
case BPF_S_ALU_OR_K:
A |= K;
continue;
case BPF_S_ALU_LSH_X:
A <<= X;
continue;
case BPF_S_ALU_LSH_K:
A <<= K;
continue;
case BPF_S_ALU_RSH_X:
A >>= X;
continue;
case BPF_S_ALU_RSH_K:
A >>= K;
continue;
case BPF_S_ALU_NEG:
A = -A;
continue;
case BPF_S_JMP_JA:
fentry += K;
continue;
case BPF_S_JMP_JGT_K:
fentry += (A > K) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JGE_K:
fentry += (A >= K) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JEQ_K:
fentry += (A == K) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JSET_K:
fentry += (A & K) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JGT_X:
fentry += (A > X) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JGE_X:
fentry += (A >= X) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JEQ_X:
fentry += (A == X) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JSET_X:
fentry += (A & X) ? fentry->jt : fentry->jf;
continue;
case BPF_S_LD_W_ABS:
k = K;
load_w:
ptr = load_pointer(skb, k, 4, &tmp);
if (ptr != NULL) {
A = get_unaligned_be32(ptr);
continue;
}
return 0;
case BPF_S_LD_H_ABS:
k = K;
load_h:
ptr = load_pointer(skb, k, 2, &tmp);
if (ptr != NULL) {
A = get_unaligned_be16(ptr);
continue;
}
return 0;
case BPF_S_LD_B_ABS:
k = K;
load_b:
ptr = load_pointer(skb, k, 1, &tmp);
if (ptr != NULL) {
A = *(u8 *)ptr;
continue;
}
return 0;
case BPF_S_LD_W_LEN:
A = skb->len;
continue;
case BPF_S_LDX_W_LEN:
X = skb->len;
continue;
case BPF_S_LD_W_IND:
k = X + K;
goto load_w;
case BPF_S_LD_H_IND:
k = X + K;
goto load_h;
case BPF_S_LD_B_IND:
k = X + K;
goto load_b;
case BPF_S_LDX_B_MSH:
ptr = load_pointer(skb, K, 1, &tmp);
if (ptr != NULL) {
X = (*(u8 *)ptr & 0xf) << 2;
continue;
}
return 0;
case BPF_S_LD_IMM:
A = K;
continue;
case BPF_S_LDX_IMM:
X = K;
continue;
case BPF_S_LD_MEM:
A = mem[K];
continue;
case BPF_S_LDX_MEM:
X = mem[K];
continue;
case BPF_S_MISC_TAX:
X = A;
continue;
case BPF_S_MISC_TXA:
A = X;
continue;
case BPF_S_RET_K:
return K;
case BPF_S_RET_A:
return A;
case BPF_S_ST:
mem[K] = A;
continue;
case BPF_S_STX:
mem[K] = X;
continue;
case BPF_S_ANC_PROTOCOL:
A = ntohs(skb->protocol);
continue;
case BPF_S_ANC_PKTTYPE:
A = skb->pkt_type;
continue;
case BPF_S_ANC_IFINDEX:
if (!skb->dev)
return 0;
A = skb->dev->ifindex;
continue;
case BPF_S_ANC_MARK:
A = skb->mark;
continue;
case BPF_S_ANC_QUEUE:
A = skb->queue_mapping;
continue;
case BPF_S_ANC_HATYPE:
if (!skb->dev)
return 0;
A = skb->dev->type;
continue;
case BPF_S_ANC_RXHASH:
A = skb->rxhash;
continue;
case BPF_S_ANC_CPU:
A = raw_smp_processor_id();
continue;
case BPF_S_ANC_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 BPF_S_ANC_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:
WARN_RATELIMIT(1, "Unknown code:%u jt:%u tf:%u k:%u\n",
fentry->code, fentry->jt,
fentry->jf, fentry->k);
return 0;
}
}
return 0;
}
EXPORT_SYMBOL(sk_run_filter);
/*
* Security :
* A BPF program is able to use 16 cells of memory to store intermediate
* values (check u32 mem[BPF_MEMWORDS] in sk_run_filter())
* As we dont want to clear mem[] array for each packet going through
* sk_run_filter(), we check that filter loaded by user never try to read
* a cell if not previously written, and we check all branches to be sure
* a malicious user doesn't try to abuse us.
*/
static int check_load_and_stores(struct sock_filter *filter, int flen)
{
u16 *masks, memvalid = 0; /* one bit per cell, 16 cells */
int pc, ret = 0;
BUILD_BUG_ON(BPF_MEMWORDS > 16);
masks = kmalloc(flen * sizeof(*masks), GFP_KERNEL);
if (!masks)
return -ENOMEM;
memset(masks, 0xff, flen * sizeof(*masks));
for (pc = 0; pc < flen; pc++) {
memvalid &= masks[pc];
switch (filter[pc].code) {
case BPF_S_ST:
case BPF_S_STX:
memvalid |= (1 << filter[pc].k);
break;
case BPF_S_LD_MEM:
case BPF_S_LDX_MEM:
if (!(memvalid & (1 << filter[pc].k))) {
ret = -EINVAL;
goto error;
}
break;
case BPF_S_JMP_JA:
/* a jump must set masks on target */
masks[pc + 1 + filter[pc].k] &= memvalid;
memvalid = ~0;
break;
case BPF_S_JMP_JEQ_K:
case BPF_S_JMP_JEQ_X:
case BPF_S_JMP_JGE_K:
case BPF_S_JMP_JGE_X:
case BPF_S_JMP_JGT_K:
case BPF_S_JMP_JGT_X:
case BPF_S_JMP_JSET_X:
case BPF_S_JMP_JSET_K:
/* a jump must set masks on targets */
masks[pc + 1 + filter[pc].jt] &= memvalid;
masks[pc + 1 + filter[pc].jf] &= memvalid;
memvalid = ~0;
break;
}
}
error:
kfree(masks);
return ret;
}
/**
* 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)
{
/*
* Valid instructions are initialized to non-0.
* Invalid instructions are initialized to 0.
*/
static const u8 codes[] = {
[BPF_ALU|BPF_ADD|BPF_K] = BPF_S_ALU_ADD_K,
[BPF_ALU|BPF_ADD|BPF_X] = BPF_S_ALU_ADD_X,
[BPF_ALU|BPF_SUB|BPF_K] = BPF_S_ALU_SUB_K,
[BPF_ALU|BPF_SUB|BPF_X] = BPF_S_ALU_SUB_X,
[BPF_ALU|BPF_MUL|BPF_K] = BPF_S_ALU_MUL_K,
[BPF_ALU|BPF_MUL|BPF_X] = BPF_S_ALU_MUL_X,
[BPF_ALU|BPF_DIV|BPF_X] = BPF_S_ALU_DIV_X,
[BPF_ALU|BPF_AND|BPF_K] = BPF_S_ALU_AND_K,
[BPF_ALU|BPF_AND|BPF_X] = BPF_S_ALU_AND_X,
[BPF_ALU|BPF_OR|BPF_K] = BPF_S_ALU_OR_K,
[BPF_ALU|BPF_OR|BPF_X] = BPF_S_ALU_OR_X,
[BPF_ALU|BPF_LSH|BPF_K] = BPF_S_ALU_LSH_K,
[BPF_ALU|BPF_LSH|BPF_X] = BPF_S_ALU_LSH_X,
[BPF_ALU|BPF_RSH|BPF_K] = BPF_S_ALU_RSH_K,
[BPF_ALU|BPF_RSH|BPF_X] = BPF_S_ALU_RSH_X,
[BPF_ALU|BPF_NEG] = BPF_S_ALU_NEG,
[BPF_LD|BPF_W|BPF_ABS] = BPF_S_LD_W_ABS,
[BPF_LD|BPF_H|BPF_ABS] = BPF_S_LD_H_ABS,
[BPF_LD|BPF_B|BPF_ABS] = BPF_S_LD_B_ABS,
[BPF_LD|BPF_W|BPF_LEN] = BPF_S_LD_W_LEN,
[BPF_LD|BPF_W|BPF_IND] = BPF_S_LD_W_IND,
[BPF_LD|BPF_H|BPF_IND] = BPF_S_LD_H_IND,
[BPF_LD|BPF_B|BPF_IND] = BPF_S_LD_B_IND,
[BPF_LD|BPF_IMM] = BPF_S_LD_IMM,
[BPF_LDX|BPF_W|BPF_LEN] = BPF_S_LDX_W_LEN,
[BPF_LDX|BPF_B|BPF_MSH] = BPF_S_LDX_B_MSH,
[BPF_LDX|BPF_IMM] = BPF_S_LDX_IMM,
[BPF_MISC|BPF_TAX] = BPF_S_MISC_TAX,
[BPF_MISC|BPF_TXA] = BPF_S_MISC_TXA,
[BPF_RET|BPF_K] = BPF_S_RET_K,
[BPF_RET|BPF_A] = BPF_S_RET_A,
[BPF_ALU|BPF_DIV|BPF_K] = BPF_S_ALU_DIV_K,
[BPF_LD|BPF_MEM] = BPF_S_LD_MEM,
[BPF_LDX|BPF_MEM] = BPF_S_LDX_MEM,
[BPF_ST] = BPF_S_ST,
[BPF_STX] = BPF_S_STX,
[BPF_JMP|BPF_JA] = BPF_S_JMP_JA,
[BPF_JMP|BPF_JEQ|BPF_K] = BPF_S_JMP_JEQ_K,
[BPF_JMP|BPF_JEQ|BPF_X] = BPF_S_JMP_JEQ_X,
[BPF_JMP|BPF_JGE|BPF_K] = BPF_S_JMP_JGE_K,
[BPF_JMP|BPF_JGE|BPF_X] = BPF_S_JMP_JGE_X,
[BPF_JMP|BPF_JGT|BPF_K] = BPF_S_JMP_JGT_K,
[BPF_JMP|BPF_JGT|BPF_X] = BPF_S_JMP_JGT_X,
[BPF_JMP|BPF_JSET|BPF_K] = BPF_S_JMP_JSET_K,
[BPF_JMP|BPF_JSET|BPF_X] = BPF_S_JMP_JSET_X,
};
int pc;
if (flen == 0 || flen > BPF_MAXINSNS)
return -EINVAL;
/* check the filter code now */
for (pc = 0; pc < flen; pc++) {
struct sock_filter *ftest = &filter[pc];
u16 code = ftest->code;
if (code >= ARRAY_SIZE(codes))
return -EINVAL;
code = codes[code];
if (!code)
return -EINVAL;
/* Some instructions need special checks */
switch (code) {
case BPF_S_ALU_DIV_K:
/* check for division by zero */
if (ftest->k == 0)
return -EINVAL;
ftest->k = reciprocal_value(ftest->k);
break;
case BPF_S_LD_MEM:
case BPF_S_LDX_MEM:
case BPF_S_ST:
case BPF_S_STX:
/* check for invalid memory addresses */
if (ftest->k >= BPF_MEMWORDS)
return -EINVAL;
break;
case BPF_S_JMP_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_S_JMP_JEQ_K:
case BPF_S_JMP_JEQ_X:
case BPF_S_JMP_JGE_K:
case BPF_S_JMP_JGE_X:
case BPF_S_JMP_JGT_K:
case BPF_S_JMP_JGT_X:
case BPF_S_JMP_JSET_X:
case BPF_S_JMP_JSET_K:
/* for conditionals both must be safe */
if (pc + ftest->jt + 1 >= flen ||
pc + ftest->jf + 1 >= flen)
return -EINVAL;
break;
case BPF_S_LD_W_ABS:
case BPF_S_LD_H_ABS:
case BPF_S_LD_B_ABS:
#define ANCILLARY(CODE) case SKF_AD_OFF + SKF_AD_##CODE: \
code = BPF_S_ANC_##CODE; \
break
switch (ftest->k) {
ANCILLARY(PROTOCOL);
ANCILLARY(PKTTYPE);
ANCILLARY(IFINDEX);
ANCILLARY(NLATTR);
ANCILLARY(NLATTR_NEST);
ANCILLARY(MARK);
ANCILLARY(QUEUE);
ANCILLARY(HATYPE);
ANCILLARY(RXHASH);
ANCILLARY(CPU);
}
}
ftest->code = code;
}
/* last instruction must be a RET code */
switch (filter[flen - 1].code) {
case BPF_S_RET_K:
case BPF_S_RET_A:
return check_load_and_stores(filter, flen);
}
return -EINVAL;
}
EXPORT_SYMBOL(sk_chk_filter);
/**
* sk_filter_release_rcu - Release a socket filter by rcu_head
* @rcu: rcu_head that contains the sk_filter to free
*/
void sk_filter_release_rcu(struct rcu_head *rcu)
{
struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
bpf_jit_free(fp);
kfree(fp);
}
EXPORT_SYMBOL(sk_filter_release_rcu);
/**
* 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;
fp->bpf_func = sk_run_filter;
err = sk_chk_filter(fp->insns, fp->len);
if (err) {
sk_filter_uncharge(sk, fp);
return err;
}
bpf_jit_compile(fp);
old_fp = rcu_dereference_protected(sk->sk_filter,
sock_owned_by_user(sk));
rcu_assign_pointer(sk->sk_filter, fp);
if (old_fp)
sk_filter_uncharge(sk, old_fp);
return 0;
}
EXPORT_SYMBOL_GPL(sk_attach_filter);
int sk_detach_filter(struct sock *sk)
{
int ret = -ENOENT;
struct sk_filter *filter;
filter = rcu_dereference_protected(sk->sk_filter,
sock_owned_by_user(sk));
if (filter) {
rcu_assign_pointer(sk->sk_filter, NULL);
sk_filter_uncharge(sk, filter);
ret = 0;
}
return ret;
}
EXPORT_SYMBOL_GPL(sk_detach_filter);