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millenniumdark
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Beetle
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背面加一段codes最好了！比如缓冲区溢出的最经典文章：《Smashing The Stack For Fun And Profit》
关键就是文章的格式!他们的格式是他们的"传世招牌"
代码： 全选
.oO Phrack 49 Oo.
Volume Seven, Issue Forty-Nine
File 14 of 16
BugTraq, r00t, and Underground.Org
bring you
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Smashing The Stack For Fun And Profit
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
by Aleph One
aleph1@underground.org
`smash the stack` [C programming] n. On many C implementations
it is possible to corrupt the execution stack by writing past
the end of an array declared auto in a routine. Code that does
this is said to smash the stack, and can cause return from the
routine to jump to a random address. This can produce some of
the most insidious data-dependent bugs known to mankind.
Variants include trash the stack, scribble the stack, mangle
the stack; the term mung the stack is not used, as this is
never done intentionally. See spam; see also alias bug,
fandango on core, memory leak, precedence lossage, overrun screw.
Introduction
~~~~~~~~~~~~
Over the last few months there has been a large increase of buffer
overflow vulnerabilities being both discovered and exploited. Examples
of these are syslog, splitvt, sendmail 8.7.5, Linux/FreeBSD mount, Xt
library, at, etc. This paper attempts to explain what buffer overflows
are, and how their exploits work.
Basic knowledge of assembly is required. An understanding of virtual
memory concepts, and experience with gdb are very helpful but not necessary.
We also assume we are working with an Intel x86 CPU, and that the operating
system is Linux.
Some basic definitions before we begin: A buffer is simply a contiguous
block of computer memory that holds multiple instances of the same data
type. C programmers normally associate with the word buffer arrays. Most
commonly, character arrays. Arrays, like all variables in C, can be
declared either static or dynamic. Static variables are allocated at load
time on the data segment. Dynamic variables are allocated at run time on
the stack. To overflow is to flow, or fill over the top, brims, or bounds.
We will concern ourselves only with the overflow of dynamic buffers, otherwise
known as stack-based buffer overflows.
Process Memory Organization
~~~~~~~~~~~~~~~~~~~~~~~~~~~
To understand what stack buffers are we must first understand how a
process is organized in memory. Processes are divided into three regions:
Text, Data, and Stack. We will concentrate on the stack region, but first
a small overview of the other regions is in order.
The text region is fixed by the program and includes code (instructions)
and read-only data. This region corresponds to the text section of the
executable file. This region is normally marked read-only and any attempt to
write to it will result in a segmentation violation.
The data region contains initialized and uninitialized data. Static
variables are stored in this region. The data region corresponds to the
data-bss sections of the executable file. Its size can be changed with the
brk(2) system call. If the expansion of the bss data or the user stack
exhausts available memory, the process is blocked and is rescheduled to
run again with a larger memory space. New memory is added between the data
and stack segments.
/------------------\ lower
| | memory
| Text | addresses
| |
|------------------|
| (Initialized) |
| Data |
| (Uninitialized) |
|------------------|
| |
| Stack | higher
| | memory
\------------------/ addresses
Fig. 1 Process Memory Regions
What Is A Stack?
~~~~~~~~~~~~~~~~
A stack is an abstract data type frequently used in computer science. A
stack of objects has the property that the last object placed on the stack
will be the first object removed. This property is commonly referred to as
last in, first out queue, or a LIFO.
Several operations are defined on stacks. Two of the most important are
PUSH and POP. PUSH adds an element at the top of the stack. POP, in
contrast, reduces the stack size by one by removing the last element at the
top of the stack.
Why Do We Use A Stack?
~~~~~~~~~~~~~~~~~~~~~~
Modern computers are designed with the need of high-level languages in
mind. The most important technique for structuring programs introduced by
high-level languages is the procedure or function. From one point of view, a
procedure call alters the flow of control just as a jump does, but unlike a
jump, when finished performing its task, a function returns control to the
statement or instruction following the call. This high-level abstraction
is implemented with the help of the stack.
The stack is also used to dynamically allocate the local variables used in
functions, to pass parameters to the functions, and to return values from the
function.
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dreamyfish
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csust
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it is very good!
but now i see it in www.taobao.com ??why??
but now i see it in www.taobao.com ??why??