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xen/9p: use alloc/free_pages_exact()

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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>
---
V4:
- new patch
This commit is contained in:
Juergen Gross 2022-03-07 09:48:55 +01:00
parent cd7bcfab4e
commit 5cadd4bb1d
1 changed files with 6 additions and 8 deletions
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14
net/9p/trans_xen.c
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@ -281,9 +281,9 @@ 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);
@ -322,8 +322,8 @@ 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;
@ -354,9 +354,7 @@ out:
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);