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dkim=none (message not signed) header.d=none;nongnu.org; dmarc=none action=none header.from=virtuozzo.com; Received: from AM7PR08MB5494.eurprd08.prod.outlook.com (2603:10a6:20b:dc::15) by AM5PR0801MB1716.eurprd08.prod.outlook.com (2603:10a6:203:39::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4087.40; Mon, 3 May 2021 12:31:32 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133%7]) with mapi id 15.20.4087.039; Mon, 3 May 2021 12:31:31 +0000 Subject: Re: [PATCH 1/2] block: Fix Transaction leak in bdrv_root_attach_child() From: Vladimir Sementsov-Ogievskiy To: Max Reitz , Kevin Wolf , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org References: <20210503110555.24001-1-kwolf@redhat.com> <20210503110555.24001-2-kwolf@redhat.com> <9e23f679-84ac-9d1a-09dc-4894cd9d6979@redhat.com> Message-ID: Date: Mon, 3 May 2021 15:31:29 +0300 User-Agent: Mozilla/5.0 (X11; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR01-HE1-obe.outbound.protection.outlook.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-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: 2.1.23 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" 03.05.2021 15:14, Vladimir Sementsov-Ogievskiy wrote: > 03.05.2021 14:53, Max Reitz wrote: >> On 03.05.21 13:51, Vladimir Sementsov-Ogievskiy wrote: >>> 03.05.2021 14:49, Max Reitz wrote: >>>> On 03.05.21 13:05, Kevin Wolf wrote: >>>>> The error path needs to call tran_finalize(), too. >>>>> >>>>> Fixes: CID 1452773 >>>>> Fixes: 548a74c0dbc858edd1a7ee3045b5f2fe710bd8b1 >>>>> Signed-off-by: Kevin Wolf >>>>> --- >>>>>   block.c | 7 ++++--- >>>>>   1 file changed, 4 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/block.c b/block.c >>>>> index 874c22c43e..5c0ced6238 100644 >>>>> --- a/block.c >>>>> +++ b/block.c >>>>> @@ -2918,13 +2918,14 @@ BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs, >>>>>                                      child_role, perm, shared_perm, opaque, >>>>>                                      &child, tran, errp); >>>>>       if (ret < 0) { >>>>> -        bdrv_unref(child_bs); >>>>> -        return NULL; >>>>> +        assert(child == NULL); >>>>> +        goto out; >>>>>       } >>>>>       ret = bdrv_refresh_perms(child_bs, errp); >>>>> -    tran_finalize(tran, ret); >>>>> +out: >>>>> +    tran_finalize(tran, ret); >>>>>       bdrv_unref(child_bs); >>>>>       return child; >>>> >>>> Looks OK, so: >>>> >>>> Reviewed-by: Max Reitz >>>> >>>> However, the function’s description says that it will return NULL on error.  But if bdrv_refresh_perms() fails, it will still return a non-NULL child.  Is that right? >>>> >>> >>> No, it's reset to NULL on transaction abort, so code is correct. It's not obvious, and I've added a comment and assertion in my version of this fix "[PATCH 1/6] block: fix leak of tran in bdrv_root_attach_child" >> >> The fact that the transaction keeps the pointer to this local variable around is a bit horrifying, but well. >> > > Yes this looks overcomplicated here. But it's useful for bdrv_set_backing_noperm where we would have to add a separate entry to @tran to rollback bs->backing change. Probably, it's better to refactor this thing. Or at least document that out-pointer argument goes into transaction, and should be valid up to transaction finalization. > > > documentation done: [PATCH 7/6] block: document child argument of bdrv_attach_child_common() -- Best regards, Vladimir