Re: [PATCH] Fix crash with "maintenance print arc"

[Andrew Burgess <aburgess@redhat.com>]

Luis Machado via Gdb-patches <gdb-patches@sourceware.org> writes:

> While doing something else, I noticed GDB crashed with
> "maintenance print arc".

I tried building current master, and "maintenance print arc" completes
just fine (for me).  Can you give more details on how to reproduce the
crash?

Thanks,
Andrew


>
> This happens because the code expects to find a "show" string pattern
> within "maintenance print arc", since "arc" here is a prefix, and skip it.
> In this case though, it won't find it, and we will have a bad pointer
> getting dereferenced.
>
> There is another part of the code with a similar assumption.
>
> This patch hardens both code paths to prevent future crashes.
>
> Regression-tested on x86_64 and aarch64 Linux Ubuntu 20.04.
> ---
>  gdb/cli/cli-setshow.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/gdb/cli/cli-setshow.c b/gdb/cli/cli-setshow.c
> index 213573e443e..3852a505cf5 100644
> --- a/gdb/cli/cli-setshow.c
> +++ b/gdb/cli/cli-setshow.c
> @@ -712,7 +712,13 @@ cmd_show_list (struct cmd_list_element *list, int from_tty)
>  	{
>  	  ui_out_emit_tuple optionlist_emitter (uiout, "optionlist");
>  	  std::string prefixname = list->prefixname ();
> -	  const char *new_prefix = strstr (prefixname.c_str (), "show ") + 5;
> +	  const char *new_prefix = strstr (prefixname.c_str (), "show ");
> +
> +	  /* If we've found a "show" string, remove it now.  */
> +	  if (new_prefix != nullptr)
> +	    new_prefix += 5;
> +	  else
> +	    new_prefix = prefixname.c_str ();
>  
>  	  if (uiout->is_mi_like_p ())
>  	    uiout->field_string ("prefix", new_prefix);
> @@ -726,8 +732,15 @@ cmd_show_list (struct cmd_list_element *list, int from_tty)
>  	    {
>  	      /* If we find a prefix, output it (with "show " skipped).  */
>  	      std::string prefixname = list->prefix->prefixname ();
> -	      prefixname = (!list->prefix->is_prefix () ? ""
> -			    : strstr (prefixname.c_str (), "show ") + 5);
> +	      const char *prefix = nullptr;
> +
> +	      if (list->prefix->is_prefix ())
> +		prefix = strstr (prefixname.c_str (), "show ");
> +
> +	      /* If we've found a "show" string, remove it now.  */
> +	      if (prefix != nullptr)
> +		prefixname = prefix + 5;
> +
>  	      uiout->text (prefixname);
>  	    }
>  	  uiout->field_string ("name", list->name);
> -- 
> 2.25.1