Re: [PATCH v3 3/4] bisect--helper: reimplement `bisect_run` shell function in C

[Junio C Hamano <gitster@pobox.com>]

Andrzej Hunt <andrzej@ahunt.org> writes:

>> +	struct strbuf command = STRBUF_INIT;
>> +	struct strvec args = STRVEC_INIT;
>> +	struct strvec run_args = STRVEC_INIT;
>> + ...
>> +	run_args.v[0] = xstrdup(command.buf);
>> +	run_args.nr = 1;
>
> AFAIUI manipulating the strvec directly like this means that we will
> violate the promise that strvec.v is always NULL-terminated. It's 
> probably safer to call 'strvec_push(run_args, command.buf)' instead of
> manipulating v and nr?

True.

> Violating the NULL-termination promise a problem because... (continued
> below)
>
>> +
>> +	while (1) {
>> +		strvec_clear(&args);
>> +		exit = 1;
>> +
>> +		printf(_("running %s"), command.buf);
>> +		res = run_command_v_opt(run_args.v, RUN_USING_SHELL);
>
> run_command_v_opt() implicitly expects a NULL-terminated list of
> strings. It's not documented in run_command_v_opt()'s comments,
> however run_command_v_opt() does explain that it's a wrapper around 
> start_command(), which uses child_process, and child_process.argv is
> documented to require a NULL-terminated list.
>
> If argv is not NULL-terminated, we hit a buffer overflow read  in
> prepare_shell_cmd(), which can be reproduced by running something
> like:
>
>   make CC=clang-11 SANITIZE=address COPTS="-Og -g" GIT_TEST_OPTS=-v
>   T=t6030-bisect-porcelain.sh test
>
> which results in ASAN reporting this error:
> ...

Thanks for a careful explanation.