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Tue, 25 Nov 2025 07:47:18 -0800 (PST) X-Google-Smtp-Source: AGHT+IGqNMDRg851SAlhx7A+zAlVRju9eh/d0GZ7ZRiEC0ty4aq3ofVDRT//COKka2xQj++tRR0gjA== X-Received: by 2002:ac8:7c53:0:b0:4e8:a850:e7db with SMTP id d75a77b69052e-4efbdad7f96mr46269661cf.71.1764085638125; Tue, 25 Nov 2025 07:47:18 -0800 (PST) Received: from x1.local ([142.188.210.156]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8b3295e4b96sm1201206185a.45.2025.11.25.07.47.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Nov 2025 07:47:17 -0800 (PST) Date: Tue, 25 Nov 2025 10:47:16 -0500 From: Peter Xu To: Markus Armbruster Cc: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , qemu-devel@nongnu.org, farosas@suse.de, peter.maydell@linaro.org Subject: Re: [PATCH] migration: Fix double-free on error path Message-ID: References: <20251125070554.2256181-1-armbru@redhat.com> <875xayxo6t.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <875xayxo6t.fsf@pond.sub.org> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.152, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Nov 25, 2025 at 01:59:54PM +0100, Markus Armbruster wrote: > Marc-André Lureau writes: > > > Hi > > > > On Tue, Nov 25, 2025 at 11:06 AM Markus Armbruster wrote: > >> > >> Fixes: ffaa1b50a879 (migration: Use warn_reportf_err() where appropriate) > >> Resolves: Coverity CID 1643463 > >> Signed-off-by: Markus Armbruster > > > > Reviewed-by: Marc-André Lureau > > > >> --- > >> migration/multifd.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/migration/multifd.c b/migration/multifd.c > >> index 6210454838..3203dc98e1 100644 > >> --- a/migration/multifd.c > >> +++ b/migration/multifd.c > >> @@ -450,7 +450,7 @@ static void multifd_send_set_error(Error *err) > >> */ > >> static void migration_ioc_shutdown_gracefully(QIOChannel *ioc) > >> { > >> - g_autoptr(Error) local_err = NULL; > >> + Error *local_err = NULL; > >> > >> if (!migration_has_failed(migrate_get_current()) && > >> object_dynamic_cast((Object *)ioc, TYPE_QIO_CHANNEL_TLS)) { > >> -- > >> 2.49.0 > >> > > > > Maybe warn_reportf_err() should take a Error **err instead, and clear > > it (and accept NULL values) > > Our deallocating functions don't work that way. > > Having them take a pointer by reference and clear it gets rid of *one* > dangling reference. There may be more. True. However I need to confess I like Marc-André's proposal.. Normally we only have one Error object, or >1 objects. The only thing I'm not sure is such design doesn't match with the error API (e.g. current form matches the more famous error_report_err(), and likely others that I'm not familiar). So at least this will need some more thoughts before all the code churns. Thanks, > > Coverity is fairly good at finding the kind of use after free this could > avoid. > > Error ** parameters are almost always for returning errors. Not having > to wonder what such a parameter is for makes code easier to read. -- Peter Xu