xen/gntalloc: don't use gnttab_query_foreign_access()

stable inclusion
from stable-v5.10.105
commit 5f36ae75b847e7f87e4144602f418a624ca074b7
bugzilla: 186480 https://gitee.com/src-openeuler/kernel/issues/I50W9S
CVE: CVE-2022-23039

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5f36ae75b847e7f87e4144602f418a624ca074b7

--------------------------------

Commit d3b6372c upstream.

Using gnttab_query_foreign_access() is unsafe, as it is racy by design.

The use case in the gntalloc driver is not needed at all. While at it
replace the call of gnttab_end_foreign_access_ref() with a call of
gnttab_end_foreign_access(), which is what is really wanted there. In
case the grant wasn't used due to an allocation failure, just free the
grant via gnttab_free_grant_reference().

This is CVE-2022-23039 / part of XSA-396.
Reported-by: NDemi Marie Obenour <demi@invisiblethingslab.com>
Signed-off-by: NJuergen Gross <jgross@suse.com>
Reviewed-by: NJan Beulich <jbeulich@suse.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NXiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/xen/gntalloc.c

@@ -169,20 +169,14 @@ static int add_grefs(struct ioctl_gntalloc_alloc_gref *op,
 		__del_gref(gref);
 	}
 
-	/* It's possible for the target domain to map the just-allocated grant
-	 * references by blindly guessing their IDs; if this is done, then
-	 * __del_gref will leave them in the queue_gref list. They need to be
-	 * added to the global list so that we can free them when they are no
-	 * longer referenced.
-	 */
-	if (unlikely(!list_empty(&queue_gref)))
-		list_splice_tail(&queue_gref, &gref_list);
 	mutex_unlock(&gref_mutex);
 	return rc;
 }
 
 static void __del_gref(struct gntalloc_gref *gref)
 {
+	unsigned long addr;
+
 	if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
 		uint8_t *tmp = kmap(gref->page);
 		tmp[gref->notify.pgoff] = 0;
@@ -196,21 +190,16 @@ static void __del_gref(struct gntalloc_gref *gref)
 	gref->notify.flags = 0;
 
 	if (gref->gref_id) {
-		if (gnttab_query_foreign_access(gref->gref_id))
-			return;
-
-		if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
-			return;
-
+		if (gref->page) {
+			addr = (unsigned long)page_to_virt(gref->page);
+			gnttab_end_foreign_access(gref->gref_id, 0, addr);
+		} else
 			gnttab_free_grant_reference(gref->gref_id);
 	}
 
 	gref_size--;
 	list_del(&gref->next_gref);
 
-	if (gref->page)
-		__free_page(gref->page);
-
 	kfree(gref);
 }