Re: [Xen-devel] [PATCH for-4.5 1/3] python/xc: Fix multiple issues in pyflask_context_to_sid()

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-11-27 at 12:34 +0000, Andrew Cooper wrote:
> The error handling from a failed memory allocation should return
> PyErr_SetFromErrno(xc_error_obj); rather than simply calling it and continuing
> to the memcpy() below, with the dest pointer being NULL.
> 
> Furthermore, the context string is simply an input parameter to the hypercall,
> and is not mutated anywhere along the way.  The error handling elsewhere in
> the function can be simplified by not duplicating it to start with.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Coverity-IDs: 1055305 1055721
> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Xen Coverity Team <coverity@xxxxxxx>

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

This would have been far more obviously correct for 4.5 if you had stuck
to fixing the issue in the first paragraph.

> ---
>  tools/python/xen/lowlevel/xc/xc.c |   21 +++------------------
>  1 file changed, 3 insertions(+), 18 deletions(-)
> 
> diff --git a/tools/python/xen/lowlevel/xc/xc.c 
> b/tools/python/xen/lowlevel/xc/xc.c
> index d95d459..c70b388 100644
> --- a/tools/python/xen/lowlevel/xc/xc.c
> +++ b/tools/python/xen/lowlevel/xc/xc.c
> @@ -2126,8 +2126,6 @@ static PyObject *pyflask_context_to_sid(PyObject *self, 
> PyObject *args,
>  {
>      xc_interface *xc_handle;
>      char *ctx;
> -    char *buf;
> -    uint32_t len;
>      uint32_t sid;
>      int ret;
>  
> @@ -2137,28 +2135,15 @@ static PyObject *pyflask_context_to_sid(PyObject 
> *self, PyObject *args,
>                                        &ctx) )
>          return NULL;
>  
> -    len = strlen(ctx);
> -
> -    buf = malloc(len);
> -    if (!buf) {
> -        errno = -ENOMEM;
> -        PyErr_SetFromErrno(xc_error_obj);
> -    }
> -    
> -    memcpy(buf, ctx, len);
> -    
>      xc_handle = xc_interface_open(0,0,0);
>      if (!xc_handle) {
> -        free(buf);
>          return PyErr_SetFromErrno(xc_error_obj);
>      }
> -    
> -    ret = xc_flask_context_to_sid(xc_handle, buf, len, &sid);
> -        
> +
> +    ret = xc_flask_context_to_sid(xc_handle, ctx, strlen(ctx), &sid);
> +
>      xc_interface_close(xc_handle);
>  
> -    free(buf);
> -    
>      if ( ret != 0 ) {
>          errno = -ret;
>          return PyErr_SetFromErrno(xc_error_obj);



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