Re: [PATCH] show-branch: fix SEGFAULT when `--current` and `--reflog` together

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Gregory

Thanks for working on this

On 19/04/2022 17:32, Gregory David wrote:
> If run `show-branch` with `--current` and `--reflog` simultaneously, a
> SEGFAULT appears.
> 
> The bug is that we read over the end of the `reflog_msg` array after
> having `append_one_rev()` for the current branch without supplying a
> convenient message to it.
> 
> It seems that it has been introduced in:
> Commit 1aa68d6735 (show-branch: --current includes the current branch.,
> 2006-01-11)
> 
> Signed-off-by: Gregory DAVID <gregory.david@p1sec.com>
> Thanks-to: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
>   builtin/show-branch.c | 20 ++++++++++++++++++++
>   1 file changed, 20 insertions(+)
> 
> diff --git a/builtin/show-branch.c b/builtin/show-branch.c
> index e12c5e80e3..892241ce0d 100644
> --- a/builtin/show-branch.c
> +++ b/builtin/show-branch.c
> @@ -812,6 +812,26 @@ int cmd_show_branch(int ac, const char **av, const
> char *prefix)
>   		}
>   		if (!has_head) {
>   			const char *name = head;
> +			struct object_id oid;
> +			char *ref;
> +			unsigned int flags = 0;
> +			char *log_msg;
> +			char *end_log_msg;
> +			timestamp_t timestamp;
> +			int tz;
> +
> +			if (!dwim_ref(*av, strlen(*av), &oid, &ref, 0))
> +				die(_("no such ref %s"), *av);
> +			if(read_ref_at(get_main_ref_store(the_repository),
> +					ref, flags, 0, i, &oid, &log_msg,
> +					&timestamp, &tz, NULL)) {
> +				end_log_msg = strchr(log_msg, '\n');
> +				if (end_log_msg)
> +					*end_log_msg = '\0';
> +			}
> +			if(log_msg == 0 || *log_msg == '\0')
> +				log_msg = xstrfmt("(none)");
> +			reflog_msg[ref_name_cnt] = xstrfmt("(%s) (current) %s",

Do we need a bounds check here? I think we're only guaranteed that 
ref_name_cnt - 1 < MAX_REVS though I found the existing code a bit hard 
to follow

Best Wishes

Phillip

> show_date(timestamp, tz, DATE_MODE(RELATIVE)), log_msg);
>   			skip_prefix(name, "refs/heads/", &name);
>   			append_one_rev(name);
>   		}