[PATCH] tools: libxl: free devpath on failure in libxl__blktap_devpath

[PATCH] tools: libxl: free devpath on failure in libxl__blktap_devpath

[Ian Campbell]

The underlying code paths in tap_ctl_create attempt to handle both
*devpath == NULL (by allocating) and *devpath != NULL (caller provided
name) and if they allocate tend to write the return immediately before
doing other potentially error generating tasks. All of which makes
handling this at a lower level rather more complicated than handling
it in the error path of libxl__bllktap_devpath.

Note that libxl__blktap_devpath initialises devpath to NULL and if the
earlier GCSPRINTF succeeds then the value is returned earlier.
Therefore if we make it to the call to tap_ctl_create then devpath is
still NULL on entry, therefore on the error path devpath is either
still NULL or has been set to a freshly allocated value by
tap_ctl_create. Since free(NULL) is fine it is sufficient to just
free(devpath).

I also considered adding a non-NULL devnull to the gc, even on
failure, but that would have required a comment to explain the
apparently strange behaviour.

Compile tested only.

CID: 1215177

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
---
 tools/libxl/libxl_blktap2.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/libxl/libxl_blktap2.c b/tools/libxl/libxl_blktap2.c
index 4f5e522..5c9a0a2 100644
--- a/tools/libxl/libxl_blktap2.c
+++ b/tools/libxl/libxl_blktap2.c
@@ -47,6 +47,7 @@ char *libxl__blktap_devpath(libxl__gc *gc,
         return devname;
     }
 
+    free(devname);
     return NULL;
 }
 
-- 
2.1.4

Re: [PATCH] tools: libxl: free devpath on failure in libxl__blktap_devpath

[Wei Liu]

On Tue, Feb 16, 2016 at 11:09:43AM +0000, Ian Campbell wrote:
> The underlying code paths in tap_ctl_create attempt to handle both
> *devpath == NULL (by allocating) and *devpath != NULL (caller provided
> name) and if they allocate tend to write the return immediately before
> doing other potentially error generating tasks. All of which makes
> handling this at a lower level rather more complicated than handling
> it in the error path of libxl__bllktap_devpath.
>

Extraneous "l" in the function name.

> Note that libxl__blktap_devpath initialises devpath to NULL and if the
> earlier GCSPRINTF succeeds then the value is returned earlier.
> Therefore if we make it to the call to tap_ctl_create then devpath is
> still NULL on entry, therefore on the error path devpath is either
> still NULL or has been set to a freshly allocated value by
> tap_ctl_create. Since free(NULL) is fine it is sufficient to just
> free(devpath).
> 
> I also considered adding a non-NULL devnull to the gc, even on
> failure, but that would have required a comment to explain the
> apparently strange behaviour.
> 
> Compile tested only.
> 
> CID: 1215177
> 
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

Acked-by: Wei Liu <wei.liu2@citrix.com>

> ---
>  tools/libxl/libxl_blktap2.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/libxl/libxl_blktap2.c b/tools/libxl/libxl_blktap2.c
> index 4f5e522..5c9a0a2 100644
> --- a/tools/libxl/libxl_blktap2.c
> +++ b/tools/libxl/libxl_blktap2.c
> @@ -47,6 +47,7 @@ char *libxl__blktap_devpath(libxl__gc *gc,
>          return devname;
>      }
>  
> +    free(devname);
>      return NULL;
>  }
>  
> -- 
> 2.1.4
> 

Re: [PATCH] tools: libxl: free devpath on failure in libxl__blktap_devpath

[Ian Jackson]

Wei Liu writes ("Re: [PATCH] tools: libxl: free devpath on failure in libxl__blktap_devpath"):
> On Tue, Feb 16, 2016 at 11:09:43AM +0000, Ian Campbell wrote:
> > The underlying code paths in tap_ctl_create attempt to handle both
> > *devpath == NULL (by allocating) and *devpath != NULL (caller provided
> > name) and if they allocate tend to write the return immediately before
> > doing other potentially error generating tasks. All of which makes
> > handling this at a lower level rather more complicated than handling
> > it in the error path of libxl__bllktap_devpath.

Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

> Extraneous "l" in the function name.

Fixed this.

Thanks,
Ian.