Re: [Xen-devel] Fix misplaced kfree from xlated_setup_gnttab_pages

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Jan 24, 2014 at 01:31:14PM -0500, Dave Jones wrote:
> Passing a freed 'pages' to free_xenballooned_pages will end badly
> on kernels with slub debug enabled.

Ouch.
> 
> This looks out of place between the rc assign and the check, and
> was likely a cut-and-paste error.
> 
> Signed-off-by: Dave Jones <davej@xxxxxxxxxxxxxxxxx>
> 
> diff --git a/arch/x86/xen/grant-table.c b/arch/x86/xen/grant-table.c
> index 103c93f874b2..28990cc97304 100644
> --- a/arch/x86/xen/grant-table.c
> +++ b/arch/x86/xen/grant-table.c
> @@ -161,12 +161,11 @@ static int __init xlated_setup_gnttab_pages(void)
>  
>       rc = arch_gnttab_map_shared(pfns, nr_grant_frames, nr_grant_frames,
>                                   &xen_auto_xlat_grant_frames.vaddr);
> -
> -     kfree(pages);
>       if (rc) {
>               pr_warn("%s Couldn't map %ld pfns rc:%d\n", __func__,
>                       nr_grant_frames, rc);
>               free_xenballooned_pages(nr_grant_frames, pages);
> +             kfree(pages);
>               kfree(pfns);
>               return rc;
>       }

Actually it should also be freed on the success path, as so:


I can squash it in, if you are OK with that?

diff --git a/arch/x86/xen/grant-table.c b/arch/x86/xen/grant-table.c
index 103c93f..c985835 100644
--- a/arch/x86/xen/grant-table.c
+++ b/arch/x86/xen/grant-table.c
@@ -162,14 +162,15 @@ static int __init xlated_setup_gnttab_pages(void)
        rc = arch_gnttab_map_shared(pfns, nr_grant_frames, nr_grant_frames,
                                    &xen_auto_xlat_grant_frames.vaddr);
 
-       kfree(pages);
        if (rc) {
                pr_warn("%s Couldn't map %ld pfns rc:%d\n", __func__,
                        nr_grant_frames, rc);
                free_xenballooned_pages(nr_grant_frames, pages);
+               kfree(pages);
                kfree(pfns);
                return rc;
        }
+       kfree(pages);
 
        xen_auto_xlat_grant_frames.pfn = pfns;
        xen_auto_xlat_grant_frames.count = nr_grant_frames;

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