Technical description
A buffer overflow occurs when data written to a buffer, due to insufficient bounds checking, corrupts data values in memory addresses adjacent to the allocated buffer. Most commonly this occurs when copying strings of characters from one buffer to another.
Basic example
In the following example, a program has defined two data items which are adjacent in memory: an 8-byte-long string buffer, A, and a two-byte integer, B. Initially, A contains nothing but zero bytes, and B contains the number 1979. Characters are one byte wide.
variable name A B
value [..............null string.............] 1979
hex value 00 00 00 00 00 00 00 00 07 BB
Now, the program attempts to store the null-terminated string "excessive" in the A buffer. By failing to check the length of the string, it overwrites the value of B:
variable name A B
value 'e' 'x' 'c' 'e' 's' 's' 'i' 'v' 25856
hex 65 78 63 65 73 73 69 76 65 00
Although the programmer did not intend to change B at all, B's value has now been replaced by a number formed from part of the character string. In this example, on a big-endian system that uses ASCII, "e" followed by a zero byte would become the number 25856. If B was the only other variable data item defined by the program, writing an even longer string that went past the end of B could cause an error such as a segmentation fault, terminating the process.
*Check ko lang sa next maintenance, kasi yong ibang source code galing Gala-Lab.
