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[2620:137:e000::1:20]) by mx.google.com with ESMTP id k20-20020a056870819400b00199aad87a98si4828470oae.215.2023.05.16.09.11.14; Tue, 16 May 2023 09:11:28 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@cirrus.com header.s=PODMain02222019 header.b=Rmr3LlMw; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=cirrus.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234513AbjEPQJa (ORCPT + 99 others); Tue, 16 May 2023 12:09:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33316 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234113AbjEPQIu (ORCPT ); Tue, 16 May 2023 12:08:50 -0400 Received: from mx0b-001ae601.pphosted.com (mx0b-001ae601.pphosted.com [67.231.152.168]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BDB8BA27F for ; Tue, 16 May 2023 09:08:31 -0700 (PDT) Received: from pps.filterd (m0077474.ppops.net [127.0.0.1]) by mx0b-001ae601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 34GFMCaf029111; Tue, 16 May 2023 11:08:00 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cirrus.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding : content-type; s=PODMain02222019; bh=+MDWXt5D6nc/s9cRAPjbV0EysPuWW1pUM4Nf/uIC2MA=; b=Rmr3LlMw/YzMnqh5fHSrsIYUIu3t91HB1bUpUMYOn/G+MCLGiFjiny3G9qkMthTeFwrh tMdvfd4OPFjixYQ+Oh/vTWM1C62ungDPRVe6eWBHQUAavqi0FpEJ+LqClY7mzy4xNiD9 p3ONybZbxk8bErJhFUYzCTwMWJ9jvjJCSP9y2ORT/Kyk3yY/z/Th4gGV9O5QryF+Z3zS qVIjk1T82+YIYwdWaKNQxUvc1nthJQKVsWQwhzQjCi65sm9bv4+GZLc37NQNuBF4gL5N wqtPlt2ofc3BAV93ApkKpu3GZI9EX1+tctQwL76CKKIfjV2mZUHMfyVqxGAey+9ThpBu 0w== Received: from ediex01.ad.cirrus.com ([84.19.233.68]) by mx0b-001ae601.pphosted.com (PPS) with ESMTPS id 3qj6ymvnvm-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 16 May 2023 11:07:59 -0500 Received: from ediex01.ad.cirrus.com (198.61.84.80) by ediex01.ad.cirrus.com (198.61.84.80) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.26; Tue, 16 May 2023 11:07:56 -0500 Received: from ediswmail.ad.cirrus.com (198.61.86.93) by ediex01.ad.cirrus.com (198.61.84.80) with Microsoft SMTP Server id 15.2.1118.26 via Frontend Transport; Tue, 16 May 2023 11:07:56 -0500 Received: from EDIN4L06LR3.ad.cirrus.com (EDIN4L06LR3.ad.cirrus.com [198.61.64.66]) by ediswmail.ad.cirrus.com (Postfix) with ESMTP id AC99111A8; Tue, 16 May 2023 16:07:56 +0000 (UTC) From: Richard Fitzgerald To: , CC: , , Richard Fitzgerald Subject: [PATCH 3/5] debugfs: Update debugfs_create_str() kerneldoc to warn about pointer race Date: Tue, 16 May 2023 17:07:51 +0100 Message-ID: <20230516160753.32317-4-rf@opensource.cirrus.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20230516160753.32317-1-rf@opensource.cirrus.com> References: <20230516160753.32317-1-rf@opensource.cirrus.com> MIME-Version: 1.0 X-Proofpoint-GUID: Of7ZDDsEtC4tmVWJr_igdUJqwZdbJ2F7 X-Proofpoint-ORIG-GUID: Of7ZDDsEtC4tmVWJr_igdUJqwZdbJ2F7 X-Proofpoint-Spam-Reason: safe X-Spam-Status: No, score=-2.7 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW,SPF_HELO_NONE,SPF_PASS, T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1766067786560976410?= X-GMAIL-MSGID: =?utf-8?q?1766067786560976410?= Add a warning to the debugfs_create_str() kerneldoc that the char * pointer value must not change after the function returns, because of a race with debugfs_read_file_str() accessing the pointer. The only safe case is a change from NULL to non-NULL because in that case debugfs_read_file_str() will see either the NULL or the valid pointer. Signed-off-by: Richard Fitzgerald --- fs/debugfs/file.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c index 0c039a3d9a42..77794871f26d 100644 --- a/fs/debugfs/file.c +++ b/fs/debugfs/file.c @@ -938,11 +938,18 @@ static const struct file_operations fops_str_wo = { * directory dentry if set. If this parameter is %NULL, then the * file will be created in the root of the debugfs filesystem. * @value: a pointer to the variable that the file should read to and write - * from. + * from. The char* pointer must not change, except from NULL to + * non-NULL. * * This function creates a file in debugfs with the given name that * contains the value of the variable @value. If the @mode variable is so * set, it can be read from, and written to. + * + * The char* pointed to by @value must not change after calling this + * function EXCEPT that it may change from NULL to non-NULL. This is to + * prevent the file read from accessing a stale pointer. A change from + * NULL to non-NULL is the only safe change, because the read will + * instantaneously see either NULL or the valid pointer. */ void debugfs_create_str(const char *name, umode_t mode, struct dentry *parent, char **value)