qcow2: check request on vmstate save/load path

We modify the request by adding an offset to vmstate. Let's check the
modified request. It will help us to safely move .bdrv_co_preadv_part
and .bdrv_co_pwritev_part to int64_t type of offset and bytes.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210903102807.27127-3-vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

block/io.c

@@ -956,7 +956,7 @@ bool coroutine_fn bdrv_make_request_serialising(BdrvTrackedRequest *req,
     return waited;
 }
 
-static int bdrv_check_qiov_request(int64_t offset, int64_t bytes,
+int bdrv_check_qiov_request(int64_t offset, int64_t bytes,
                             QEMUIOVector *qiov, size_t qiov_offset,
                             Error **errp)
 {

block/qcow2.c

@@ -5227,24 +5227,55 @@ static int qcow2_has_zero_init(BlockDriverState *bs)
     }
 }
 
+/*
+ * Check the request to vmstate. On success return
+ *      qcow2_vm_state_offset(bs) + @pos
+ */
+static int64_t qcow2_check_vmstate_request(BlockDriverState *bs,
+                                           QEMUIOVector *qiov, int64_t pos)
+{
+    BDRVQcow2State *s = bs->opaque;
+    int64_t vmstate_offset = qcow2_vm_state_offset(s);
+    int ret;
+
+    /* Incoming requests must be OK */
+    bdrv_check_qiov_request(pos, qiov->size, qiov, 0, &error_abort);
+
+    if (INT64_MAX - pos < vmstate_offset) {
+        return -EIO;
+    }
+
+    pos += vmstate_offset;
+    ret = bdrv_check_qiov_request(pos, qiov->size, qiov, 0, NULL);
+    if (ret < 0) {
+        return ret;
+    }
+
+    return pos;
+}
+
 static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
                               int64_t pos)
 {
-    BDRVQcow2State *s = bs->opaque;
+    int64_t offset = qcow2_check_vmstate_request(bs, qiov, pos);
+    if (offset < 0) {
+        return offset;
+    }
 
     BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_SAVE);
-    return bs->drv->bdrv_co_pwritev_part(bs, qcow2_vm_state_offset(s) + pos,
+    return bs->drv->bdrv_co_pwritev_part(bs, offset, qiov->size, qiov, 0, 0);
-                                         qiov->size, qiov, 0, 0);
 }
 
 static int qcow2_load_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
                               int64_t pos)
 {
-    BDRVQcow2State *s = bs->opaque;
+    int64_t offset = qcow2_check_vmstate_request(bs, qiov, pos);
+    if (offset < 0) {
+        return offset;
+    }
 
     BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_LOAD);
-    return bs->drv->bdrv_co_preadv_part(bs, qcow2_vm_state_offset(s) + pos,
+    return bs->drv->bdrv_co_preadv_part(bs, offset, qiov->size, qiov, 0, 0);
-                                        qiov->size, qiov, 0, 0);
 }
 
 /*

include/block/block_int.h

@@ -94,6 +94,9 @@ typedef struct BdrvTrackedRequest {
     struct BdrvTrackedRequest *waiting_for;
 } BdrvTrackedRequest;
 
+int bdrv_check_qiov_request(int64_t offset, int64_t bytes,
+                            QEMUIOVector *qiov, size_t qiov_offset,
+                            Error **errp);
 int bdrv_check_request(int64_t offset, int64_t bytes, Error **errp);
 
 struct BlockDriver {