diff options
Diffstat (limited to 'release/src/linux/linux/net/ipv4/netfilter/ipt_u32.c')
| -rw-r--r-- | release/src/linux/linux/net/ipv4/netfilter/ipt_u32.c | 211 |
1 files changed, 211 insertions, 0 deletions
diff --git a/release/src/linux/linux/net/ipv4/netfilter/ipt_u32.c b/release/src/linux/linux/net/ipv4/netfilter/ipt_u32.c new file mode 100644 index 00000000..0c749563 --- /dev/null +++ b/release/src/linux/linux/net/ipv4/netfilter/ipt_u32.c @@ -0,0 +1,211 @@ +/* Kernel module to match u32 packet content. */ + +/* +U32 tests whether quantities of up to 4 bytes extracted from a packet +have specified values. The specification of what to extract is general +enough to find data at given offsets from tcp headers or payloads. + + --u32 tests + The argument amounts to a program in a small language described below. + tests := location = value | tests && location = value + value := range | value , range + range := number | number : number + a single number, n, is interpreted the same as n:n + n:m is interpreted as the range of numbers >=n and <=m + location := number | location operator number + operator := & | << | >> | @ + + The operators &, <<, >>, && mean the same as in c. The = is really a set + membership operator and the value syntax describes a set. The @ operator + is what allows moving to the next header and is described further below. + + *** Until I can find out how to avoid it, there are some artificial limits + on the size of the tests: + - no more than 10 ='s (and 9 &&'s) in the u32 argument + - no more than 10 ranges (and 9 commas) per value + - no more than 10 numbers (and 9 operators) per location + + To describe the meaning of location, imagine the following machine that + interprets it. There are three registers: + A is of type char*, initially the address of the IP header + B and C are unsigned 32 bit integers, initially zero + + The instructions are: + number B = number; + C = (*(A+B)<<24)+(*(A+B+1)<<16)+(*(A+B+2)<<8)+*(A+B+3) + &number C = C&number + <<number C = C<<number + >>number C = C>>number + @number A = A+C; then do the instruction number + Any access of memory outside [skb->head,skb->end] causes the match to fail. + Otherwise the result of the computation is the final value of C. + + Whitespace is allowed but not required in the tests. + However the characters that do occur there are likely to require + shell quoting, so it's a good idea to enclose the arguments in quotes. + +Example: + match IP packets with total length >= 256 + The IP header contains a total length field in bytes 2-3. + --u32 "0&0xFFFF=0x100:0xFFFF" + read bytes 0-3 + AND that with FFFF (giving bytes 2-3), + and test whether that's in the range [0x100:0xFFFF] + +Example: (more realistic, hence more complicated) + match icmp packets with icmp type 0 + First test that it's an icmp packet, true iff byte 9 (protocol) = 1 + --u32 "6&0xFF=1 && ... + read bytes 6-9, use & to throw away bytes 6-8 and compare the result to 1 + Next test that it's not a fragment. + (If so it might be part of such a packet but we can't always tell.) + n.b. This test is generally needed if you want to match anything + beyond the IP header. + The last 6 bits of byte 6 and all of byte 7 are 0 iff this is a complete + packet (not a fragment). Alternatively, you can allow first fragments + by only testing the last 5 bits of byte 6. + ... 4&0x3FFF=0 && ... + Last test: the first byte past the IP header (the type) is 0 + This is where we have to use the @syntax. The length of the IP header + (IHL) in 32 bit words is stored in the right half of byte 0 of the + IP header itself. + ... 0>>22&0x3C@0>>24=0" + The first 0 means read bytes 0-3, + >>22 means shift that 22 bits to the right. Shifting 24 bits would give + the first byte, so only 22 bits is four times that plus a few more bits. + &3C then eliminates the two extra bits on the right and the first four + bits of the first byte. + For instance, if IHL=5 then the IP header is 20 (4 x 5) bytes long. + In this case bytes 0-1 are (in binary) xxxx0101 yyzzzzzz, + >>22 gives the 10 bit value xxxx0101yy and &3C gives 010100. + @ means to use this number as a new offset into the packet, and read + four bytes starting from there. This is the first 4 bytes of the icmp + payload, of which byte 0 is the icmp type. Therefore we simply shift + the value 24 to the right to throw out all but the first byte and compare + the result with 0. + +Example: + tcp payload bytes 8-12 is any of 1, 2, 5 or 8 + First we test that the packet is a tcp packet (similar to icmp). + --u32 "6&0xFF=6 && ... + Next, test that it's not a fragment (same as above). + ... 0>>22&0x3C@12>>26&0x3C@8=1,2,5,8" + 0>>22&3C as above computes the number of bytes in the IP header. + @ makes this the new offset into the packet, which is the start of the + tcp header. The length of the tcp header (again in 32 bit words) is + the left half of byte 12 of the tcp header. The 12>>26&3C + computes this length in bytes (similar to the IP header before). + @ makes this the new offset, which is the start of the tcp payload. + Finally 8 reads bytes 8-12 of the payload and = checks whether the + result is any of 1, 2, 5 or 8 +*/ + +#include <linux/module.h> +#include <linux/skbuff.h> + +#include <linux/netfilter_ipv4/ipt_u32.h> +#include <linux/netfilter_ipv4/ip_tables.h> + +/* #include <asm-i386/timex.h> for timing */ + +MODULE_AUTHOR("Don Cohen <don@isis.cs3-inc.com>"); +MODULE_DESCRIPTION("IP tables u32 matching module"); +MODULE_LICENSE("GPL"); + +static int +match(const struct sk_buff *skb, + const struct net_device *in, + const struct net_device *out, + const void *matchinfo, + int offset, + const void *hdr, + u_int16_t datalen, + int *hotdrop) +{ + const struct ipt_u32 *data = matchinfo; + int testind, i; + unsigned char* origbase = (char*)skb->nh.iph; + unsigned char* base = origbase; + unsigned char* head = skb->head; + unsigned char* end = skb->end; + int nnums, nvals; + u_int32_t pos, val; + /* unsigned long long cycles1, cycles2, cycles3, cycles4; + cycles1 = get_cycles(); */ + + for (testind=0; testind < data->ntests; testind++) { + base = origbase; /* reset for each test */ + pos = data->tests[testind].location[0].number; + if (base+pos+3 > end || base+pos < head) + return 0; + val = (base[pos]<<24) + (base[pos+1]<<16) + + (base[pos+2]<<8) + base[pos+3]; + nnums = data->tests[testind].nnums; + for (i=1; i < nnums; i++) { + u_int32_t number = data->tests[testind].location[i].number; + switch (data->tests[testind].location[i].nextop) { + case IPT_U32_AND: + val = val & number; + break; + case IPT_U32_LEFTSH: + val = val << number; + break; + case IPT_U32_RIGHTSH: + val = val >> number; + break; + case IPT_U32_AT: + base = base + val; + pos = number; + if (base+pos+3 > end || base+pos < head) + return 0; + val = (base[pos]<<24) + (base[pos+1]<<16) + + (base[pos+2]<<8) + base[pos+3]; + break; + } + } + nvals = data->tests[testind].nvalues; + for (i=0; i < nvals; i++) { + if ((data->tests[testind].value[i].min <= val) && + (val <= data->tests[testind].value[i].max)) { + break; + } + } + if (i >= data->tests[testind].nvalues) { + /* cycles2 = get_cycles(); + printk("failed %d in %d cycles\n", testind, + cycles2-cycles1); */ + return 0; + } + } + /* cycles2 = get_cycles(); + printk("succeeded in %d cycles\n", cycles2-cycles1); */ + return 1; +} + +static int +checkentry(const char *tablename, + const struct ipt_ip *ip, + void *matchinfo, + unsigned int matchsize, + unsigned int hook_mask) +{ + if (matchsize != IPT_ALIGN(sizeof(struct ipt_u32))) + return 0; + return 1; +} + +static struct ipt_match u32_match += { { NULL, NULL }, "u32", &match, &checkentry, NULL, THIS_MODULE }; + +static int __init init(void) +{ + return ipt_register_match(&u32_match); +} + +static void __exit fini(void) +{ + ipt_unregister_match(&u32_match); +} + +module_init(init); +module_exit(fini); |