From 8357d75bfdb85ea63253cf369f405830c7b13d78 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Fri, 25 Feb 2022 16:05:42 +0100 Subject: [PATCH] xen/9p: use alloc/free_pages_exact() Commit 5cadd4bb1d7fc9ab201ac14620d1a478357e4ebd upstream. Instead of __get_free_pages() and free_pages() use alloc_pages_exact() and free_pages_exact(). This is in preparation of a change of gnttab_end_foreign_access() which will prohibit use of high-order pages. By using the local variable "order" instead of ring->intf->ring_order in the error path of xen_9pfs_front_alloc_dataring() another bug is fixed, as the error path can be entered before ring->intf->ring_order is being set. By using alloc_pages_exact() the size in bytes is specified for the allocation, which fixes another bug for the case of order < (PAGE_SHIFT - XEN_PAGE_SHIFT). This is part of CVE-2022-23041 / XSA-396. Reported-by: Simon Gaiser Signed-off-by: Juergen Gross Reviewed-by: Jan Beulich Signed-off-by: Greg Kroah-Hartman --- net/9p/trans_xen.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c index 3ec1a51a6944..432ac5a16f2e 100644 --- a/net/9p/trans_xen.c +++ b/net/9p/trans_xen.c @@ -304,9 +304,9 @@ static void xen_9pfs_front_free(struct xen_9pfs_front_priv *priv) ref = priv->rings[i].intf->ref[j]; gnttab_end_foreign_access(ref, 0, 0); } - free_pages((unsigned long)priv->rings[i].data.in, - priv->rings[i].intf->ring_order - - (PAGE_SHIFT - XEN_PAGE_SHIFT)); + free_pages_exact(priv->rings[i].data.in, + 1UL << (priv->rings[i].intf->ring_order + + XEN_PAGE_SHIFT)); } gnttab_end_foreign_access(priv->rings[i].ref, 0, 0); free_page((unsigned long)priv->rings[i].intf); @@ -345,8 +345,8 @@ static int xen_9pfs_front_alloc_dataring(struct xenbus_device *dev, if (ret < 0) goto out; ring->ref = ret; - bytes = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, - order - (PAGE_SHIFT - XEN_PAGE_SHIFT)); + bytes = alloc_pages_exact(1UL << (order + XEN_PAGE_SHIFT), + GFP_KERNEL | __GFP_ZERO); if (!bytes) { ret = -ENOMEM; goto out; @@ -377,9 +377,7 @@ static int xen_9pfs_front_alloc_dataring(struct xenbus_device *dev, if (bytes) { for (i--; i >= 0; i--) gnttab_end_foreign_access(ring->intf->ref[i], 0, 0); - free_pages((unsigned long)bytes, - ring->intf->ring_order - - (PAGE_SHIFT - XEN_PAGE_SHIFT)); + free_pages_exact(bytes, 1UL << (order + XEN_PAGE_SHIFT)); } gnttab_end_foreign_access(ring->ref, 0, 0); free_page((unsigned long)ring->intf);