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Re: nbd: bitmap_to_extents() calls nbd_extent_array_add() without checki

From: Eric Blake
Subject: Re: nbd: bitmap_to_extents() calls nbd_extent_array_add() without checking return value: coverity false positive?
Date: Fri, 6 Nov 2020 14:35:58 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0

On 11/6/20 11:22 AM, Peter Maydell wrote:
> Hi; Coverity's "you usually check the return value of this function
> but you didn't do that here" heuristic has fired on the code in
> nbd/server.c:bitmap_to_extents() -- the function nbd_extent_array_add()
> is called five times in server.c, and the return value is checked
> in four of those, but not in the final call at the end of
> bitmap_to_extents(). (CID 1436125.)
> Is this a false positive, or should the caller be handling an
> error here ?

False positive, but I don't mind tweaking the code to silence Coverity.
This should do it; let me know if I should turn it into a formal patch.

diff --git i/nbd/server.c w/nbd/server.c
index d145e1a69083..377698a2ce85 100644
--- i/nbd/server.c
+++ w/nbd/server.c
@@ -2128,9 +2128,8 @@ static void bitmap_to_extents(BdrvDirtyBitmap *bitmap,

-    if (!full) {
-        /* last non dirty extent */
-        nbd_extent_array_add(es, end - start, 0);
+    if (!full && nbd_extent_array_add(es, end - start, 0) < 0) {
+        /* last non dirty extent, not a problem if array is now full */


Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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