NFS: Use ERR_CAST() to avoid cross-structure cast

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>
Acked-by: Trond Myklebust <trond.myklebust@primarydata.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index 1a224a33a6c23c362e1bbacb8150bb9bbf02b3fd..e5686be67be8d361a32344e3aaaae235d739ffd7 100644 (file)
--- a/fs/nfs/namespace.c
+++ b/fs/nfs/namespace.c
@@ -246,7 +246,7 @@ struct vfsmount *nfs_do_submount(struct dentry *dentry, struct nfs_fh *fh,
 
        devname = nfs_devname(dentry, page, PAGE_SIZE);
        if (IS_ERR(devname))
-               mnt = (struct vfsmount *)devname;
+               mnt = ERR_CAST(devname);
        else
                mnt = nfs_do_clone_mount(NFS_SB(dentry->d_sb), devname, &mountdata);