1 libfido2 can be fuzzed using AFL or libFuzzer, with or without
4 AFL is more convenient when fuzzing the path from the authenticator to
5 libfido2 in an existing application. To do so, use preload-snoop.c with a real
6 authenticator to obtain an initial corpus, rebuild libfido2 with -DFUZZ=ON, and
7 use preload-fuzz.c to read device data from stdin.
9 libFuzzer is better suited for bespoke fuzzers; see fuzz_cred.c, fuzz_credman.c,
10 fuzz_assert.c, fuzz_hid.c, and fuzz_mgmt.c for examples. To build these
11 harnesses, use -DCMAKE_C_FLAGS=-fsanitize=fuzzer-no-link
12 -DFUZZ_LDFLAGS=-fsanitize=fuzzer -DFUZZ=ON.
14 If -DFUZZ=ON is enabled, symbols listed in wrapped.sym are wrapped in the
15 resulting shared object. The wrapper functions simulate failure according to a
16 deterministic RNG and probabilities defined in wrap.c. Harnesses wishing to
17 use this functionality should call prng_init() with a seed obtained from the
18 corpus. To mutate only the seed part of a libFuzzer harness's corpora,
19 use '-reduce_inputs=0 --fido-mutate=seed'.
21 To run under ASAN/MSAN/UBSAN, libfido2 needs to be linked against flavours of
22 libcbor and OpenSSL built with the respective sanitiser. In order to keep
23 memory utilisation at a manageable level, you can either enforce limits at
24 the OS level (e.g. cgroups on Linux), or patch libcbor with the diff below.
25 N.B., the patch below is relative to libcbor 0.10.1.
27 diff --git src/cbor/internal/memory_utils.c src/cbor/internal/memory_utils.c
28 index bbea63c..3f7c9af 100644
29 --- src/cbor/internal/memory_utils.c
30 +++ src/cbor/internal/memory_utils.c
31 @@ -41,7 +41,11 @@ size_t _cbor_safe_signaling_add(size_t a, size_t b) {
33 void* _cbor_alloc_multiple(size_t item_size, size_t item_count) {
34 if (_cbor_safe_to_multiply(item_size, item_count)) {
35 - return _cbor_malloc(item_size * item_count);
36 + if (item_count > 1000) {
39 + return _cbor_malloc(item_size * item_count);