Re: [PATCH v3] argp-help: Get rid of alloca.

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 13/09/23 13:00, Joe Simmons-Talbott wrote:
> Replace alloca with malloc and a scratch_buffer to avoid potential stack
> overflow.
> 
> Checked on x86_64-linux-gnu
> ---
>  argp/argp-help.c | 40 ++++++++++++++++++++++------------------
>  1 file changed, 22 insertions(+), 18 deletions(-)
> 
> diff --git a/argp/argp-help.c b/argp/argp-help.c
> index d019ed58d2..54a15a8233 100644
> --- a/argp/argp-help.c
> +++ b/argp/argp-help.c
> @@ -25,21 +25,7 @@
>  #include <config.h>
>  #endif
>  
> -/* AIX requires this to be the first thing in the file.  */
> -#ifndef __GNUC__
> -# if HAVE_ALLOCA_H || defined _LIBC
> -#  include <alloca.h>
> -# else
> -#  ifdef _AIX
> -#pragma alloca
> -#  else
> -#   ifndef alloca /* predefined by HP cc +Olibcalls */
> -char *alloca ();
> -#   endif
> -#  endif
> -# endif
> -#endif
> -
> +#include <scratch_buffer.h>
>  #include <stdbool.h>
>  #include <stddef.h>
>  #include <stdlib.h>
> @@ -1450,8 +1436,14 @@ hol_usage (struct hol *hol, argp_fmtstream_t stream)
>      {
>        unsigned nentries;
>        struct hol_entry *entry;
> -      char *short_no_arg_opts = alloca (strlen (hol->short_options) + 1);
> -      char *snao_end = short_no_arg_opts;
> +      char *short_no_arg_opts;
> +      char *snao_end;
> +
> +      short_no_arg_opts = malloc (strlen (hol->short_options) + 1);
> +      assert (short_no_arg_opts != NULL);
> +
> +      snao_end = short_no_arg_opts;
> +	
>  
>        /* First we put a list of short options without arguments.  */
>        for (entry = hol->entries, nentries = hol->num_entries
> @@ -1478,6 +1470,8 @@ hol_usage (struct hol *hol, argp_fmtstream_t stream)
>  	   ; entry++, nentries--)
>  	hol_entry_long_iterate (entry, usage_long_opt,
>  				entry->argp->argp_domain, stream);
> +
> +      free (short_no_arg_opts);
>      }
>  }
>  \f
> @@ -1698,7 +1692,15 @@ _help (const struct argp *argp, const struct argp_state *state, FILE *stream,
>      {
>        int first_pattern = 1, more_patterns;
>        size_t num_pattern_levels = argp_args_levels (argp);
> -      char *pattern_levels = alloca (num_pattern_levels);
> +      struct scratch_buffer buf;
> +      scratch_buffer_init (&buf);
> +      char *pattern_levels;
> +      bool result;
> +
> +      result = scratch_buffer_set_array_size (&buf, 1, num_pattern_levels);
> +      assert (result);
> +
> +      pattern_levels = buf.data;
>  
>        memset (pattern_levels, 0, num_pattern_levels);
>  


Use malloc here as well.

> @@ -1746,6 +1748,8 @@ _help (const struct argp *argp, const struct argp_state *state, FILE *stream,
>  	  first_pattern = 0;
>  	}
>        while (more_patterns);
> +
> +      scratch_buffer_free (&buf);
>      }
>  
>    if (flags & ARGP_HELP_PRE_DOC)