Re: [PATCH 08/13 v4] libxl: don't leak ptr in libxl_list_vm error case

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 02/12/13 11:05, Matthew Daley wrote:
> While at it, tidy up the function; there's no point in allocating more
> than the amount of domains actually returned by xc_domain_getinfolist
> (unless 0 domains are returned, in which case we should still allocate
> one libxl_vminfo struct so we can return a non-NULL result and not
> appear to have failed from the caller's perspective.)
>
> Coverity-ID: 1055888
> Signed-off-by: Matthew Daley <mattd@bugfuzz.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

> ---
> v4: Add a comment describing the calloc malarkey
>
>  tools/libxl/libxl.c |   19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index b112294..7308d44 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -674,17 +674,22 @@ libxl_vminfo * libxl_list_vm(libxl_ctx *ctx, int *nb_vm_out)
>      libxl_vminfo *ptr;
>      int idx, i, ret;
>      xc_domaininfo_t info[1024];
> -    int size = 1024;
>  
> -    ptr = calloc(size, sizeof(libxl_vminfo));
> -    if (!ptr)
> +    ret = xc_domain_getinfolist(ctx->xch, 1, ARRAY_SIZE(info), info);
> +    if (ret < 0) {
> +        LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR, "getting domain info list");
>          return NULL;
> +    }
>  
> -    ret = xc_domain_getinfolist(ctx->xch, 1, 1024, info);
> -    if (ret<0) {
> -        LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR, "geting domain info list");
> +    /*
> +     * Always make sure to allocate at least one element; if we don't and we
> +     * request zero, we (might) get back a null pointer, which if returned
> +     * to our caller will make them think we've failed
> +     */
> +    ptr = calloc(ret ? ret : 1, sizeof(libxl_vminfo));
> +    if (!ptr)
>          return NULL;
> -    }
> +
>      for (idx = i = 0; i < ret; i++) {
>          if (libxl_is_stubdom(ctx, info[i].domain, NULL))
>              continue;