Patch-mainline: v5.17
Git-commit: 33172ab50a53578a95691310f49567c9266968b0
References: bsc#1196488, XSA-396, CVE-2022-23038
From: Juergen Gross <jgross@suse.com>
Date: Mon, 7 Mar 2022 09:48:54 +0100
Subject: [PATCH] xen/scsifront: don't use gnttab_query_foreign_access() for
 mapped status

It isn't enough to check whether a grant is still being in use by
calling gnttab_query_foreign_access(), as a mapping could be realized
by the other side just after having called that function.

In case the call was done in preparation of revoking a grant it is
better to do so via gnttab_try_end_foreign_access() and check the
success of that operation instead.

This is CVE-2022-23038 / part of XSA-396.

Reported-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
V2:
- use gnttab_try_end_foreign_access()
---
 drivers/scsi/xen-scsifront.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/scsi/xen-scsifront.c b/drivers/scsi/xen-scsifront.c
index 12c10a5e3d93..7f421600cb66 100644
--- a/drivers/scsi/xen-scsifront.c
+++ b/drivers/scsi/xen-scsifront.c
@@ -233,12 +233,11 @@ static void scsifront_gnttab_done(struct vscsifrnt_info *info,
 		return;
 
 	for (i = 0; i < shadow->nr_grants; i++) {
-		if (unlikely(gnttab_query_foreign_access(shadow->gref[i]))) {
+		if (unlikely(!gnttab_try_end_foreign_access(shadow->gref[i]))) {
 			shost_printk(KERN_ALERT, info->host, KBUILD_MODNAME
 				     "grant still in use by backend\n");
 			BUG();
 		}
-		gnttab_end_foreign_access(shadow->gref[i], 0, 0UL);
 	}
 
 	kfree(shadow->sg);
-- 
2.34.1