[PATCH 4.9 20/29] xen/blkfront: fix leaking data in shared pages

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Roger Pau Monne <roger.pau@citrix.com>

commit 2f446ffe9d737e9a844b97887919c4fda18246e7 upstream.

When allocating pages to be used for shared communication with the
backend always zero them, this avoids leaking unintended data present
on the pages.

This is CVE-2022-26365, part of XSA-403.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/block/xen-blkfront.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -297,7 +297,7 @@ static int fill_grant_buffer(struct blkf
 			goto out_of_memory;
 
 		if (info->feature_persistent) {
-			granted_page = alloc_page(GFP_NOIO);
+			granted_page = alloc_page(GFP_NOIO | __GFP_ZERO);
 			if (!granted_page) {
 				kfree(gnt_list_entry);
 				goto out_of_memory;
@@ -1729,7 +1729,7 @@ static int setup_blkring(struct xenbus_d
 	for (i = 0; i < info->nr_ring_pages; i++)
 		rinfo->ring_ref[i] = GRANT_INVALID_REF;
 
-	sring = alloc_pages_exact(ring_size, GFP_NOIO);
+	sring = alloc_pages_exact(ring_size, GFP_NOIO | __GFP_ZERO);
 	if (!sring) {
 		xenbus_dev_fatal(dev, -ENOMEM, "allocating shared ring");
 		return -ENOMEM;
@@ -2311,7 +2311,8 @@ static int blkfront_setup_indirect(struc
 
 		BUG_ON(!list_empty(&rinfo->indirect_pages));
 		for (i = 0; i < num; i++) {
-			struct page *indirect_page = alloc_page(GFP_NOIO);
+			struct page *indirect_page = alloc_page(GFP_NOIO |
+			                                        __GFP_ZERO);
 			if (!indirect_page)
 				goto out_of_memory;
 			list_add(&indirect_page->lru, &rinfo->indirect_pages);