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diff --git a/docs/fuzzing_in_depth.md b/docs/fuzzing_in_depth.md index 4481bce6..19d8e783 100644 --- a/docs/fuzzing_in_depth.md +++ b/docs/fuzzing_in_depth.md @@ -13,6 +13,43 @@ Fuzzing source code is a three-step process: 3. Perform the fuzzing of the target by randomly mutating input and assessing if a generated input was processed in a new path in the target binary. +### 0. Common sense risks + +Please keep in mind that, similarly to many other computationally-intensive +tasks, fuzzing may put a strain on your hardware and on the OS. In particular: + +- Your CPU will run hot and will need adequate cooling. In most cases, if + cooling is insufficient or stops working properly, CPU speeds will be + automatically throttled. That said, especially when fuzzing on less suitable + hardware (laptops, smartphones, etc.), it's not entirely impossible for + something to blow up. + +- Targeted programs may end up erratically grabbing gigabytes of memory or + filling up disk space with junk files. AFL++ tries to enforce basic memory + limits, but can't prevent each and every possible mishap. The bottom line is + that you shouldn't be fuzzing on systems where the prospect of data loss is + not an acceptable risk. + +- Fuzzing involves billions of reads and writes to the filesystem. On modern + systems, this will be usually heavily cached, resulting in fairly modest + "physical" I/O - but there are many factors that may alter this equation. It + is your responsibility to monitor for potential trouble; with very heavy I/O, + the lifespan of many HDDs and SSDs may be reduced. + + A good way to monitor disk I/O on Linux is the `iostat` command: + + ```shell + $ iostat -d 3 -x -k [...optional disk ID...] + ``` + + Using the `AFL_TMPDIR` environment variable and a RAM-disk, you can have the + heavy writing done in RAM to prevent the aforementioned wear and tear. For + example, the following line will run a Docker container with all this preset: + + ```shell + # docker run -ti --mount type=tmpfs,destination=/ramdisk -e AFL_TMPDIR=/ramdisk aflplusplus/aflplusplus + ``` + ### 1. Instrumenting the target #### a) Selecting the best AFL++ compiler for instrumenting the target |