From: Andrzej Hunt Date: Tue, 04 May 2021 17:23:22 GMT Subject: Re: [PATCH v7 10/28] reftable: (de)serialization for the polymorphic record type. Message-ID: In-Reply-To: <028dd13e701bf82523cc6da1e68a9dab480c1b27.1618832277.git.gitgitgadget@gmail.com> On 19/04/2021 13:37, Han-Wen Nienhuys via GitGitGadget wrote: > From: Han-Wen Nienhuys [...snip...] > diff --git a/reftable/record.c b/reftable/record.c > new file mode 100644 > index 000000000000..b111852b667e > --- /dev/null > +++ b/reftable/record.c[...snip...> +static void reftable_obj_record_copy_from(void *rec, const void *src_rec, > + int hash_size) > +{ > + struct reftable_obj_record *obj = rec; > + const struct reftable_obj_record *src = > + (const struct reftable_obj_record *)src_rec; > + int olen; > + > + reftable_obj_record_release(obj); > + *obj = *src; > + obj->hash_prefix = reftable_malloc(obj->hash_prefix_len); > + memcpy(obj->hash_prefix, src->hash_prefix, obj->hash_prefix_len); > + > + olen = obj->offset_len * sizeof(uint64_t); > + obj->offsets = reftable_malloc(olen); > + memcpy(obj->offsets, src->offsets, olen); > +} If src->offset_len is 0 then offsets will be NULL - and passing NULL into memcpy() results in undefined behaviour. I think we should either add an "if (src->offset_len)" check around the memcpy, or perhaps switch to COPY_ARRAY() which performs that check for us. (We can probably also skip the malloc and hence also olen calculation in this scenario though, because obj->offsets should already be NULL if src->offsets was NULL?) Specifically, if I run t0032 as such: make CC=clang-11 UBSAN_OPTIONS=print_stacktrace=1 SANITIZE=undefined COPTS="-Og -g" GIT_TEST_OPTS=-v T=t0032-reftable-unittest.sh test UBSAN reports the following error: reftable/record.c:475:23: runtime error: null pointer passed as argument 2, which is declared to never be null /usr/include/string.h:43:28: note: nonnull attribute specified here #0 0x698e52 in reftable_obj_record_copy_from record.c:475:2 #1 0x6ac806 in test_copy record_test.c:21:2 #2 0x6abb73 in test_reftable_obj_record_roundtrip record_test.c:334:3 #3 0x6abb73 in record_test_main record_test.c:403:2 #4 0x437f08 in cmd__reftable test-reftable.c:10:2 #5 0x427e74 in cmd_main test-tool.c:126:11 #6 0x428043 in main common-main.c:52:11 #7 0x7f3cd1044349 in __libc_start_main (/lib64/libc.so.6+0x24349) #8 0x407209 in _start start.S:120 SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior reftable/record.c:475:23 in [...snip...] > +static int reftable_obj_record_decode(void *rec, struct strbuf key, > + uint8_t val_type, struct string_view in, > + int hash_size) > +{ > + struct string_view start = in; > + struct reftable_obj_record *r = rec; > + uint64_t count = val_type; > + int n = 0; > + uint64_t last; > + int j; > + r->hash_prefix = reftable_malloc(key.len); > + memcpy(r->hash_prefix, key.buf, key.len); > + r->hash_prefix_len = key.len; > + > + if (val_type == 0) { > + n = get_var_int(&count, &in); > + if (n < 0) { > + return n; > + } > + > + string_view_consume(&in, n); > + } > + > + r->offsets = NULL; > + r->offset_len = 0; > + if (count == 0) > + return start.len - in.len; And it looks like creating a reftable_obj_record with offsets = NULL and offset_len = 0 is considered valid based on the code above. [... snipped the rest ...]