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SubjectRe: [PATCH v2] NFS: Avoid cross-structure casting
On Wed, Apr 5, 2017 at 8:29 AM, Kees Cook <keescook@chromium.org> wrote:
> When the call to nfs_devname() fails, the error path attempts to retain
> the error via the mnt variable, but this requires a cast across very
> different types (char * to struct vfsmount *), which the upcoming
> structure layout randomization plugin flags as being potentially
> dangerous in the face of randomization. This is a false positive, but
> what this code actually wants to do is retain the error value, so this
> patch explicitly sets it, instead of using what seems to be an
> unexpected cast.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>

If I can get an Acked-by on this, I could push it via the gcc-plugin tree.

Thanks!

-Kees

> ---
> v2: duh, use ERR_CAST. thanks neilb!
> ---
> fs/nfs/namespace.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
> index 786f17580582..8ca5d147124d 100644
> --- a/fs/nfs/namespace.c
> +++ b/fs/nfs/namespace.c
> @@ -259,9 +259,10 @@ struct vfsmount *nfs_do_submount(struct dentry *dentry, struct nfs_fh *fh,
> if (page == NULL)
> goto out;
> devname = nfs_devname(dentry, page, PAGE_SIZE);
> - mnt = (struct vfsmount *)devname;
> - if (IS_ERR(devname))
> + if (IS_ERR(devname)) {
> + mnt = ERR_CAST(devname);
> goto free_page;
> + }
> mnt = nfs_do_clone_mount(NFS_SB(dentry->d_sb), devname, &mountdata);
> free_page:
> free_page((unsigned long)page);
> --
> 2.7.4
>
>
> --
> Kees Cook
> Pixel Security



--
Kees Cook
Pixel Security

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