|author||Yasuyuki KOZAKAI <firstname.lastname@example.org>||2007-11-29 04:59:51 +0000|
|committer||Yasuyuki KOZAKAI <email@example.com>||2007-11-29 04:59:51 +0000|
libxt_u32.man already exists.
Diffstat (limited to 'extensions')
1 files changed, 0 insertions, 129 deletions
diff --git a/extensions/libip6t_u32.man b/extensions/libip6t_u32.man
deleted file mode 100644
@@ -1,129 +0,0 @@
-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.
-[\fB!\fR]\fB --u32 \fItests\fR
-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, \fIn\fR, is interpreted the same as \fIn:n\fR. \fIn:m\fR is
-interpreted as the range of numbers \fB>=n\fR and \fB<=m\fR.
-.IP "" 4
-location := number | location operator number
-.IP "" 4
-operator := "&" | "<<" | ">>" | "@"
-The operators \fB&\fR, \fB<<\fR, \fB>>\fR and \fB&&\fR mean the same as in C.
-The \fB=\fR is really a set membership operator and the value syntax describes
-a set. The \fB@\fR operator is what allows moving to the next header and is
-described further below.
-There are currently some artificial implementation limits on the size of the
-.IP " *"
-no more than 10 of "\fB=\fR" (and 9 "\fB&&\fR"s) in the u32 argument
-.IP " *"
-no more than 10 ranges (and 9 commas) per value
-.IP " *"
-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 \fBchar *\fR, 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->data,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 is a good idea
-to enclose the arguments in quotes.
-match IP packets with total length >= 256
-The IP header contains a total length field in bytes 2-3.
---u32 "\fB0 & 0xFFFF = 0x100:0xFFFF\fR"
-read bytes 0-3
-AND that with 0xFFFF (giving bytes 2-3), and test whether that is in the range
-Example: (more realistic, hence more complicated)
-match ICMP packets with icmp type 0
-First test that it is an ICMP packet, true iff byte 9 (protocol) = 1
---u32 "\fB6 & 0xFF = 1 &&\fR ...
-read bytes 6-9, use \fB&\fR to throw away bytes 6-8 and compare the result to
-1. Next test that it is not a fragment. (If so, it might be part of such a
-packet but we cannot 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.
- ... \fB4 & 0x3FFF = 0 &&\fR ...
-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.
- ... \fB0 >> 22 & 0x3C @ 0 >> 24 = 0\fR"
-The first 0 means read bytes 0-3, \fB>>22\fR 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. \fB&3C\fR 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, \fB>>22\fR gives the 10 bit value xxxx0101yy and
-\fB&3C\fR gives 010100. \fB@\fR 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.
-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 "\fB6 & 0xFF = 6 &&\fR ...
-Next, test that it is not a fragment (same as above).
- ... \fB0 >> 22 & 0x3C @ 12 >> 26 & 0x3C @ 8 = 1,2,5,8\fR"
-\fB0>>22&3C\fR as above computes the number of bytes in the IP header. \fB@\fR
-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 \fB12>>26&3C\fR 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
-\fB=\fR checks whether the result is any of 1, 2, 5 or 8.