[PATCH v2] rtems-fdt / shell - Fix string truncation warning

[Chris Johns]

OK to push.

Thanks
Chris

On 20/10/20 12:16 am, Frank Kuehndel wrote:
> From: Frank Kühndel <frank.kuehndel at embedded-brains.de>
> 
> The compiler warning was:
> 
> ../../../cpukit/libmisc/rtems-fdt/rtems-fdt.c:267:5: warning:
> 'strncpy' specified bound depends on the length of the source argument
>   267 |     strncpy(path, name, namelen);
>       |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> It turns out that the `strncpy()` nor the buffer `path` is needed when
> one uses `strncmp()` instead of `strcmp()`. This needs some change to
> the algorithm but has the advantage that `name` is never truncated
> to the size of the buffer `path`.
> ---
>  cpukit/libmisc/rtems-fdt/rtems-fdt.c | 40 +++++++++++++---------------
>  1 file changed, 19 insertions(+), 21 deletions(-)
> 
> diff --git a/cpukit/libmisc/rtems-fdt/rtems-fdt.c b/cpukit/libmisc/rtems-fdt/rtems-fdt.c
> index 39e70bffec..0ea365314f 100644
> --- a/cpukit/libmisc/rtems-fdt/rtems-fdt.c
> +++ b/cpukit/libmisc/rtems-fdt/rtems-fdt.c
> @@ -248,48 +248,46 @@ rtems_fdt_index_find_by_name(rtems_fdt_index* index,
>  {
>    int         min = 0;
>    int         max = index->num_entries;
> -  char        path[256];
> -  const char* cmp_name = name;
> -
>    /*
>     * Handle trailing slash case.
>     */
> -  int namelen = strlen(name);
> +  size_t namelen = strlen(name);
>    if (namelen > 0 && name[namelen-1] == '/')
>    {
>      namelen--;
> -
> -    if (namelen >= (int)sizeof(path) - 1)
> -    {
> -      namelen = sizeof(path) - 1;
> -    }
> -
> -    strncpy(path, name, namelen);
> -    path[namelen] = 0;
> -    cmp_name = path;
>    }
>  
>    /* Binary search for the name. */
>    while (min < max)
>    {
>      int middle = (min + max) / 2;
> -    int cmp = strcmp(cmp_name, index->entries[middle].name);
> +    int cmp = strncmp(name, index->entries[middle].name, namelen);
> +    if (cmp == 0)
> +    {
> +      /* 'namelen' characters are equal but 'index->entries[middle].name' */
> +      /* could have additional characters. */
> +      if (index->entries[middle].name[namelen] == '\0')
> +      {
> +        /* Found it. */
> +        return index->entries[middle].offset;
> +      }
> +      else
> +      {
> +         /* 'index->entries[middle].name' is longer than 'name'. */
> +         cmp = -1;
> +      }
> +    }
>      if (cmp < 0)
>      {
>        /* Look lower than here. */
>        max = middle;
>      }
> -    else if (cmp > 0)
> +    else
>      {
>        /* Look higher than here. */
>        min = middle + 1;
>      }
> -    else
> -    {
> -      /* Found it. */
> -      return index->entries[middle].offset;
> -    }
> -  }
> + }
>  
>    /* Didn't find it. */
>    return -FDT_ERR_NOTFOUND;
>