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Fri, 5 Nov 2021 12:17:31 +0000 Date: Fri, 5 Nov 2021 15:17:15 +0300 From: Dan Carpenter To: YE Chengfeng Cc: "krzysztof.kozlowski@canonical.com" , "davem@davemloft.net" , "wengjianfeng@yulong.com" , "kuba@kernel.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: nfc: pn533: suspected double free when pn533_fill_fragment_skbs() return value <= 0 Message-ID: <20211105121715.GB2026@kadam> References: Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-ClientProxiedBy: JN2P275CA0009.ZAFP275.PROD.OUTLOOK.COM (2603:1086:0:3::21) To MWHPR1001MB2365.namprd10.prod.outlook.com (2603:10b6:301:2d::28) MIME-Version: 1.0 Received: from kadam (102.222.70.114) by JN2P275CA0009.ZAFP275.PROD.OUTLOOK.COM (2603:1086:0:3::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4669.11 via Frontend Transport; Fri, 5 Nov 2021 12:17:26 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: bbd4c891-37b0-46a0-2a1e-08d9a0563d4c X-MS-TrafficTypeDiagnostic: MWHPR10MB1662: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:4125; 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Specifically it clears out the &dev->fragment_skb list and then returns the length of the list "skb_queue_len(&dev->fragment_skb)" which is now zero. Returning success on transmit failure is fine because the network stack thinks it was lost somewhere in the network and resends it. But probably it should return -ENOMEM? But changing the return would make the other caller into a double free now. So probably the correct fix is to 1) Make pn533_fill_fragment_skbs() return -ENOMEM on error 2) Don't call dev_kfree_skb(skb); on error in pn533_fill_fragment_skbs(). Only call it on the success path. 3) Change the callers to check for negatives instead of <= 0 > We will provide patch for them after confirmation. Sounds great. You can fix it however you want. My ideas are a suggestion only. regards, dan carpenter