Fuzzing with the sample streams leads to lots of crashes about h264bitstream

[pallas]

Ok, at least one issue is in find_nal_unit, which can over read its buffer. Patch coming soon, although I need to take a break at the moment.

[pallas]

Also, NAL_UNIT_TYPE_SUBSET_SPS in read_nal_unit shallow copies sps_subset into sps_subset_table, causing a double free.

[aizvorski]

@pallas That is exceptional work - thank you!

If you find any input sequences which cause a crash/buffer overrun, I should be able to tell how (and fix it).

Note: this has been fuzzed before, but a very long time ago, circa 2012. The bs_read_* functions can safely (try to) read past the end of the existing buffer, they just read an infinite string of 0's - this is one of the main mechanisms protecting against overruns. I suspect that there could be issues in code which bypasses bs_read (mainly because of performance reasons).

[pallas]

Thanks, I've got some patches coming. One question: it looks like the .in.c files are not in sync with the .c files.. should I be updating .in.c and regenerating or should I just update the .cs directly?

[pallas]

Ok, I found a few different issues and now the fuzzer has been running for half an hour with no new error paths. I'm going to let it run overnight, refine my patches, & likely will make a PR tomorrow.

[pallas]

I'm seeing similar issues in read_pred_weight_table and read_slice_header, at least the debug versions, and at least one more double free somewhere (later assert failure in malloc, so no backtrace).

[pallas]

Ok, I've lost my momentum to keep working on this. The following functions have array overrun problems and/or double-frees post the PR I made a few weeks ago.

read_debug_dec_ref_pic_marking
read_debug_pred_weight_table
read_debug_ref_pic_list_reordering
read_debug_slice_header
read_debug_slice_header_in_scalable_extension
read_debug_slice_layer_rbsp

You can run the fuzzer by

CC=/usr/bin/afl-clang-fast CXX=/usr/bin/afl-clang-fast++ ./configure --disable-debug --disable-shared
env AFL_HARDEN=1 make
env AFL_SKIP_CPUFREQ=1 afl-fuzz -i samples/ -o results/ ./h264_analyze -p @@

I'm analyzing the results with

mkdir -p traces/
for i in results/crashes/id* ; do echo $i && valgrind --track-origins=yes  ./h264_analyze -p $i 2>&1 | tee traces/$(basename $i).out ; done
ag -H 'of size' traces/ -C 10| grep \\.c: | sed s,^.\\\+0x,0x, | sed s,^.\[^:\]\\\+:,, | sort | uniq -c

[pallas]

Hey, it seems pretty obvious that I gave up on this. Basically, ever time a dynamically sized array is created/used/destroyed, the bounds are never checked. I'm going to go ahead and close since I don't intend to do any more work here.