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RAM Disks and Saving Your SSD From AFL Fuzzing |
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Présentation : The American Fuzzy Lop fuzzer has become a critical tool for finding security vulnerabilities in all sorts of software. It has the ability to send fuzzing data through programs on the order of hundreds of millions of executions per day on a capable system, and can certainly put strain on your hardware and OS. If you are fuzzing a target program with the AFL mode where a file is written and the target binary reads from this file, then AFL is going to conduct a huge number of writes to the local disk. For a solid-state drive this can reduce its life expectancy because of write amplification. My main workstation is a Mac running OS X Yosemite, and I run a lot of Linux, FreeBSD, and OpenBSD virtual machines under Parallels for development purposes. The drive on this system is an SSD which keeps everything quite fast, but I don't want to prematurely shorten its life through huge AFL fuzzing runs. Normally, I'm using AFL to fuzz fwknop from an Ubuntu-14.10 VM, and what is needed is a way to keep disk writes down. The solution is to use a RAM disk from within the VM. First, from the Ubuntu VM, let's get set up for AFL fuzzing and show what the disk writes look like without using a RAM disk from the perspective of the host OS X system. This assumes AFL 0.89 has been installed already and is in the current path git clone https github.com mrash fwknop.git fwknop.git cd fwknop.git . autogen.sh cd test afl . compile afl-compile.sh We're not running AFL yet. Now, from the Mac, launch the Activity Monitor under Applications Utilities and look at current disk utilization AFL not running disk writes So, not terrible - currently 31 writes per second at the time the snapshot was taken, and that includes OS X itself and the VM at the same time. But, now let's fire up AFL using the digest cache wrapper on the Ubuntu VM the main AFL text UI is not shown for brevity . fuzzing-wrappers server-digest-cache.sh All right - fork server is up. All test cases processed. Here are some useful stats Test case count 1 favored, 0 variable, 1 total Bitmap range 727 to 727 bits average 727.00 bits Exec timing 477 to 477 us average 477 us All set and ready to roll And now let's take a look at disk writes again from OS X AFL no RAM disk writes Whoa, that's a massive difference - nearly two orders of magnitude. AFL has caused disk writes to spike to over 2,700 per second with total data written averaging at 19.5MB sec. Long term fuzzing at this level of disk writes would clearly present a problem for the SSD - AFL frequently needs to be left running for days on end in order to be thorough. So, let's switch everything over to use a RAM disk on the Ubuntu VM instead and see if that reduces disk writes mkdir tmp afl-ramdisk chmod 777 tmp afl-ramdisk mount -t tmpfs -o size 512M tmpfs tmp afl-ramdisk mv fwknop.git tmp afl-ramdisk cd tmp afl-ramdisk fwknop.git test afl . fuzzing-wrappers server-digest-cache.sh Here is disk utilization once again from the Mac AFL RAM disk writes We're back to less than 10 writes per second to the SSD even though AFL is going strong on the Ubuntu VM not shown . The writes for the previous fuzzing run are still shown to the left of the graph since they haven't quite aged out yet when the screenshot was taken , and new writes are so low they don't even make it above the X-axis at this scale. Although the total execs per second - about 2,000 - achieved by AFL is not appreciably faster under the RAM disk, the main benefit is that my SSD will last a lot longer. For those that don't run AFL underneath a VM, a similar strategy should still apply on the main OS. Assuming enough RAM is available for whatever software you want to fuzz, just create a RAM disk and run everything from it and extend the life of your hard drive in the process.
Les mots clés de la revue de presse pour cet article : fuzzing
Les videos sur SecuObs pour les mots clés : fuzzing
Les mots clés pour les articles publiés sur SecuObs : fuzzing
Les derniers articles du site "cipherdyne.org System and Network Security" :
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- NAT and Single Packet Authorization
- Single Packet Authorization Threat Modeling
- RAM Disks and Saving Your SSD From AFL Fuzzing
- Integrating fwknop with the 'American Fuzzy Lop' Fuzzer
- Software Release fwknop-2.6.4
- Code Coverage Challenges For Open Source Projects
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