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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jan Beulich <jbeulich@suse.com>,
        Juergen Gross <jgross@suse.com>
Subject: [PATCH 4.9 44/49] xen-blkback: dont "handle" error by BUG()
Date:   Mon, 22 Feb 2021 13:36:42 +0100
Message-Id: <20210222121028.145787329@linuxfoundation.org>
In-Reply-To: <20210222121022.546148341@linuxfoundation.org>
References: <20210222121022.546148341@linuxfoundation.org>
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From: Jan Beulich <jbeulich@suse.com>

commit 5a264285ed1cd32e26d9de4f3c8c6855e467fd63 upstream.

In particular -ENOMEM may come back here, from set_foreign_p2m_mapping().
Don't make problems worse, the more that handling elsewhere (together
with map's status fields now indicating whether a mapping wasn't even
attempted, and hence has to be considered failed) doesn't require this
odd way of dealing with errors.

This is part of XSA-362.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: stable@vger.kernel.org
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-blkback/blkback.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -860,10 +860,8 @@ again:
 			break;
 	}
 
-	if (segs_to_map) {
+	if (segs_to_map)
 		ret = gnttab_map_refs(map, NULL, pages_to_gnt, segs_to_map);
-		BUG_ON(ret);
-	}
 
 	/*
 	 * Now swizzle the MFN in our domain with the MFN from the other domain
@@ -878,7 +876,7 @@ again:
 				pr_debug("invalid buffer -- could not remap it\n");
 				put_free_pages(ring, &pages[seg_idx]->page, 1);
 				pages[seg_idx]->handle = BLKBACK_INVALID_HANDLE;
-				ret |= 1;
+				ret |= !ret;
 				goto next;
 			}
 			pages[seg_idx]->handle = map[new_map_idx].handle;