[Qemu-block] [PATCH] block/iscsi: avoid data corruption with cache=writeback

[Peter Lieven]

nb_cls_shrunk in iscsi_allocmap_update can become -1 if the
request starts and ends within the same cluster. This results
in passing -1 to bitmap_set and bitmap_clear and they don't
handle negative values properly. In the end this leads to data
corruption.

Fixes: e1123a3b40a1a9a625a29c8ed4debb7e206ea690
Cc: address@hidden
Signed-off-by: Peter Lieven <address@hidden>
---
 block/iscsi.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/block/iscsi.c b/block/iscsi.c
index 6aeeb9e..1860f1b 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -499,14 +499,18 @@ iscsi_allocmap_update(IscsiLun *iscsilun, int64_t 
sector_num,
     if (allocated) {
         bitmap_set(iscsilun->allocmap, cl_num_expanded, nb_cls_expanded);
     } else {
-        bitmap_clear(iscsilun->allocmap, cl_num_shrunk, nb_cls_shrunk);
+        if (nb_cls_shrunk > 0) {
+            bitmap_clear(iscsilun->allocmap, cl_num_shrunk, nb_cls_shrunk);
+        }
     }
 
     if (iscsilun->allocmap_valid == NULL) {
         return;
     }
     if (valid) {
-        bitmap_set(iscsilun->allocmap_valid, cl_num_shrunk, nb_cls_shrunk);
+        if (nb_cls_shrunk > 0) {
+            bitmap_set(iscsilun->allocmap_valid, cl_num_shrunk, nb_cls_shrunk);
+        }
     } else {
         bitmap_clear(iscsilun->allocmap_valid, cl_num_expanded,
                      nb_cls_expanded);
-- 
1.9.1