Re: [PATCH v7 23/28] Reftable support for git-core

[Andrzej Hunt <andrzej@ahunt.org>]

On 19/04/2021 13:37, Han-Wen Nienhuys via GitGitGadget wrote:
> From: Han-Wen Nienhuys <hanwen@google.com>
[...snip...]> diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
> new file mode 100644
> index 000000000000..55d053e5ca65
> --- /dev/null
> +++ b/refs/reftable-backend.c
[...snip...]
> +static int write_transaction_table(struct reftable_writer *writer, void *arg)
> +{
> +	struct ref_transaction *transaction = (struct ref_transaction *)arg;
> +	struct git_reftable_ref_store *refs =
> +		(struct git_reftable_ref_store *)transaction->ref_store;
> +	struct reftable_stack *stack =
> +		stack_for(refs, transaction->updates[0]->refname);
> +	uint64_t ts = reftable_stack_next_update_index(stack);
> +	int err = 0;
> +	int i = 0;
> +	struct reftable_log_record *logs =
> +		calloc(transaction->nr, sizeof(*logs));
> +	struct ref_update **sorted =
> +		malloc(transaction->nr * sizeof(struct ref_update *));
> +	struct reftable_merged_table *mt = reftable_stack_merged_table(stack);
> +	struct reftable_table tab = {NULL};
> +	struct reftable_ref_record ref = {NULL};
> +	reftable_table_from_merged_table(&tab, mt);
> +	COPY_ARRAY(sorted, transaction->updates, transaction->nr);
> +	QSORT(sorted, transaction->nr, ref_update_cmp);
> +	reftable_writer_set_limits(writer, ts, ts);
> +
> +	for (i = 0; i < transaction->nr; i++) {
> +		struct ref_update *u = sorted[i];
> +		struct reftable_log_record *log = &logs[i];
> +		struct object_id old_id;
> +		fill_reftable_log_record(log);
> +		log->update_index = ts;
> +		log->value_type = REFTABLE_LOG_UPDATE;
> +		log->refname = (char *)u->refname;
> +		log->update.new_hash = u->new_oid.hash;
> +		log->update.message = u->msg;
> +
> +		err = reftable_table_read_ref(&tab, u->refname, &ref);
> +		if (err < 0)
> +			goto done;
> +		else if (err > 0) {
> +			old_id = null_oid;
> +		} else {
> +			oidread(&old_id, ref.value.val1);
> +		}

This seems to assume that 'ref.value_type == REFTABLE_REF_VAL1' - but do 
we expect to have to handle the other types 
(REFTABLE_REF_VAL2/REFTABLE_REF_SYMREF)? When I run tests in seen 
against ASAN I see the following errors in t0031, which suggests we're 
running this code against REFTABLE_REF_SYMREF too - but I don't know if 
that means that this code should be able to handle the other ref types 
or if there's a bug higher up the stack. (AFAIUI REFTABLE_REF_DELETION 
is already handled because reftable_table_read_ref() already returns 1 
for deletion, but the other cases seem valid?)

ASAN error output:

==25352==ERROR: AddressSanitizer: heap-buffer-overflow on address 
0x603000003353 at pc 0x000000499d17 bp 0x7fff0ea0a210 sp 0x7fff0ea099d8
READ of size 32 at 0x603000003353 thread T0
     #0 0x499d16 in __asan_memcpy 
../projects/compiler-rt/lib/asan/asan_interceptors_memintrinsics.cpp:22:3
     #1 0x97ed0a in oidread hash.h:292:2
     #2 0x97ed0a in write_transaction_table refs/reftable-backend.c:548:4
     #3 0xb5537a in reftable_addition_add reftable/stack.c:650:8
     #4 0x97b024 in git_reftable_transaction_finish 
refs/reftable-backend.c:618:9
     #5 0x95f9bf in ref_transaction_commit refs.c:2218:8
     #6 0x9d3aa6 in update_head_with_reflog sequencer.c:1138:6
     #7 0x52ffbf in cmd_commit builtin/commit.c:1814:6
     #8 0x4ce8fe in run_builtin git.c:461:11
     #9 0x4ccbc8 in handle_builtin git.c:718:3
     #10 0x4cb0cc in run_argv git.c:785:4
     #11 0x4cb0cc in cmd_main git.c:916:19
     #12 0x6beded in main common-main.c:52:11
     #13 0x7f415c762349 in __libc_start_main (/lib64/libc.so.6+0x24349)
     #14 0x420769 in _start ../sysdeps/x86_64/start.S:120

0x603000003353 is located 0 bytes to the right of 19-byte region 
[0x603000003340,0x603000003353)
allocated by thread T0 here:
     #0 0x4868b4 in strdup 
../projects/compiler-rt/lib/asan/asan_interceptors.cpp:452:3
     #1 0xaa08e8 in xstrdup wrapper.c:29:14
     #2 0xb4b280 in reftable_ref_record_copy_from reftable/record.c:229:23
     #3 0xb46754 in merged_iter_next_entry reftable/merged.c:132:2
     #4 0xb46754 in merged_iter_next reftable/merged.c:141:13
     #5 0xb46754 in merged_iter_next_void reftable/merged.c:157:9
     #6 0xb500ae in iterator_next reftable/generic.c:147:9
     #7 0xb500ae in reftable_iterator_next_ref reftable/generic.c:134:9
     #8 0xb500ae in reftable_table_read_ref reftable/generic.c:46:8
     #9 0x97ec67 in write_transaction_table refs/reftable-backend.c:542:9
     #10 0xb5537a in reftable_addition_add reftable/stack.c:650:8
     #11 0x97b024 in git_reftable_transaction_finish 
refs/reftable-backend.c:618:9
     #12 0x95f9bf in ref_transaction_commit refs.c:2218:8
     #13 0x9d3aa6 in update_head_with_reflog sequencer.c:1138:6
     #14 0x52ffbf in cmd_commit builtin/commit.c:1814:6
     #15 0x4ce8fe in run_builtin git.c:461:11
     #16 0x4ccbc8 in handle_builtin git.c:718:3
     #17 0x4cb0cc in run_argv git.c:785:4
     #18 0x4cb0cc in cmd_main git.c:916:19
     #19 0x6beded in main common-main.c:52:11
     #20 0x7f415c762349 in __libc_start_main (/lib64/libc.so.6+0x24349)

SUMMARY: AddressSanitizer: heap-buffer-overflow 
../projects/compiler-rt/lib/asan/asan_interceptors_memintrinsics.cpp:22:3 in 
__asan_memcpy


Produced using:

   make CC=clang-11 SANITIZE=address COPTS="-Og -g" GIT_TEST_OPTS=-v 
T=t0031-reftable.sh test


> +
> +		/* XXX fold together with the old_id check below? */
> +
> +		log->update.old_hash = old_id.hash;
> +		if (u->flags & REF_LOG_ONLY) {
> +			continue;
> +		}
> +
> +		if (u->flags & REF_HAVE_NEW) {
> +			struct reftable_ref_record ref = { NULL };
> +			struct object_id peeled;
> +
> +			int peel_error = peel_object(&u->new_oid, &peeled);
> +			ref.refname = (char *)u->refname;
> +			ref.update_index = ts;
> +
> +			if (!peel_error) {
> +				ref.value_type = REFTABLE_REF_VAL2;
> +				ref.value.val2.target_value = peeled.hash;
> +				ref.value.val2.value = u->new_oid.hash;
> +			} else if (!is_null_oid(&u->new_oid)) {
> +				ref.value_type = REFTABLE_REF_VAL1;
> +				ref.value.val1 = u->new_oid.hash;
> +			}
> +
> +			err = reftable_writer_add_ref(writer, &ref);
> +			if (err < 0) {
> +				goto done;
> +			}
> +		}
> +	}
> +
> +	for (i = 0; i < transaction->nr; i++) {
> +		err = reftable_writer_add_log(writer, &logs[i]);
> +		clear_reftable_log_record(&logs[i]);
> +		if (err < 0) {
> +			goto done;
> +		}
> +	}
> +
> +done:
> +	assert(err != REFTABLE_API_ERROR);
> +	reftable_ref_record_release(&ref);
> +	free(logs);
> +	free(sorted);
> +	return err;
> +}
> +

[...snip...]