[PATCH 4.14 29/31] xen/9p: use alloc/free_pages_exact()

Greg Kroah-Hartman
2022-03-10T14:26:29Z

From: Juergen Gross <jgross@suse.com>

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 <simon@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/9p/trans_xen.c | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)

--- a/net/9p/trans_xen.c
+++ b/net/9p/trans_xen.c
@@ -301,9 +301,9 @@ static void xen_9pfs_front_free(struct x
ref = priv->rings[i].intf->ref[j];
gnttab_end_foreign_access(ref, 0, 0);
}
- free_pages((unsigned long)priv->rings[i].data.in,
- XEN_9PFS_RING_ORDER -
- (PAGE_SHIFT - XEN_PAGE_SHIFT));
+ free_pages_exact(priv->rings[i].data.in,
+ 1UL << (XEN_9PFS_RING_ORDER +
+ XEN_PAGE_SHIFT));
}
gnttab_end_foreign_access(priv->rings[i].ref, 0, 0);
free_page((unsigned long)priv->rings[i].intf);
@@ -341,8 +341,8 @@ static int xen_9pfs_front_alloc_dataring
if (ret < 0)
goto out;
ring->ref = ret;
- bytes = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
- XEN_9PFS_RING_ORDER - (PAGE_SHIFT - XEN_PAGE_SHIFT));
+ bytes = alloc_pages_exact(1UL << (XEN_9PFS_RING_ORDER + XEN_PAGE_SHIFT),
+ GFP_KERNEL | __GFP_ZERO);
if (!bytes) {
ret = -ENOMEM;
goto out;
@@ -373,9 +373,7 @@ out:
if (bytes) {
for (i--; i >= 0; i--)
gnttab_end_foreign_access(ring->intf->ref[i], 0, 0);
- free_pages((unsigned long)bytes,
- XEN_9PFS_RING_ORDER -
- (PAGE_SHIFT - XEN_PAGE_SHIFT));
+ free_pages_exact(bytes, 1UL << (XEN_9PFS_RING_ORDER + XEN_PAGE_SHIFT));
}
gnttab_end_foreign_access(ring->ref, 0, 0);
free_page((unsigned long)ring->intf);