Re: [PATCH unionfs 3/3] Don't use strncat() with length derived from source string

[Jessica Clarke]

On 26 Apr 2021, at 18:08, Sergey Bugaev <bugaevc@gmail.com> wrote:
> 
> This fixes Wstringop-overflow and Wstringop-truncation GCC warnings.
> See https://gcc.gnu.org/bugzilla//show_bug.cgi?id=88059
> 
> Also, fix a bug where a string was not properly null-terminated.
> ---
> lib.c  | 4 ++--
> stow.c | 5 +++--
> 2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/lib.c b/lib.c
> index 01cdbd0..717979b 100644
> --- a/lib.c
> +++ b/lib.c
> @@ -151,8 +151,8 @@ make_filepath (char *path, char *filename)
>   if (filepath == NULL) 
>     return NULL;
> 
> -  strncpy (filepath, path, length);
> -  strncat (filepath, filename, strlen (filename));
> +  strcpy (filepath, path);
> +  strcat (filepath, filename);

This is dubious. We should be using safe interfaces where possible.

>   return filepath;
> }
> diff --git a/stow.c b/stow.c
> index 812d33b..adfcf53 100644
> --- a/stow.c
> +++ b/stow.c
> @@ -282,14 +282,15 @@ stow_diradd (char *dir, int flags, struct patternlist 
> *patternlist,
>     {
>       char *tmp;
> 
> -      tmp = (char *) malloc (dir_len + 1);
> +      tmp = (char *) malloc (dir_len + 2);
> 
>       if (tmp == NULL)
>       return ENOMEM;
> 
> -      strncpy (tmp, dir, dir_len);
> +      strcpy (tmp, dir);
> 
>       tmp[dir_len] = '/';
> +      tmp[dir_len + 1] = 0;

Similarly dubious dropping of explicit lengths.

Jess