Although some double free vulnerabilities are not much more complicated than the previous example, most are spread out across hundreds of lines of code or even different files. Programmers seem particularly susceptible to freeing global variables more than once.
To illustrate why it is bad practice to allocate memory without freeing it, consider what would happen if an application were designed to run autonomously for very long time, say that application was used in the PID loop controlling the cruise control on your car. And, in that application there was un-freed memory, and that after 3 hours of running, the memory available in the microprocessor is exhausted, causing the PID to suddenly rail. "Ah!", you say, "This will never happen!" Yes, it does. (look here). (not exactly the same problem, but you get the idea)
Self-emancipation was the act of an enslaved person freeing him or herself from the bondage of slavery. If allowed, the easiest way of self-emancipation was to pay your slaveholder for your freedom, which many tradesmen and urban slaves were able to do. There are several other stories of the various ways to escape enslavement but the most extreme was by death.
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Freeing a block alters the contents of the block. Do not expect tofind any data (such as a pointer to the next block in a chain of blocks) inthe block after freeing it. Copy whatever you need out of the block beforefreeing it! Here is an example of the proper way to free all the blocks ina chain, and the strings that they point to: 350c69d7ab