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[2620:137:e000::1:20]) by mx.google.com with ESMTP id bc25-20020a056402205900b005020d16209bsi12799353edb.518.2023.03.27.11.32.08; Mon, 27 Mar 2023 11:32:31 -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=@kernel.org header.s=k20201202 header.b=XYk0XCa2; 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=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232314AbjC0SXH (ORCPT + 99 others); Mon, 27 Mar 2023 14:23:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33796 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229805AbjC0SXD (ORCPT ); Mon, 27 Mar 2023 14:23:03 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 13E3C2D5F; Mon, 27 Mar 2023 11:23:02 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 9D0AA61472; Mon, 27 Mar 2023 18:23:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A12ADC4339C; Mon, 27 Mar 2023 18:22:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1679941381; bh=fQqYYZBl6thY1SMZV6P0vcEwNdRfXWrP08DeYYxt4Z4=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=XYk0XCa2T9KN0jiczq2OUcwgvM6ftE5qrh2oytwSHElilB5OysWGRNQKhQHR5+mGF 26IEnVWANUwnUwUUejP3CJFuY9QY9KT18RUhxOrktdChTF3CrnGzt+Lst6xa1DhdTy TM5LaVPZtU7qYU7jDlEi+9tJImyIEi9zoT+I2fBgS+nf/p0gxY1aqip3MDNeGxZ1yl gRa+5VWI8JzSO2n7g8oLFaqiYW7KcfZxqhhWWI1TksZ+6WijfOrvJ5usf6Edm/Ovul yja1yO7e4XNCUcQLK8gEfx1GsohSQqkvRp4LF6W5wlgMPRqJx4e1susWo32zgXOLnk 31onql7BRgMVA== From: Christian Brauner Date: Mon, 27 Mar 2023 20:22:51 +0200 Subject: [PATCH 1/3] pid: add pidfd_prepare() MIME-Version: 1.0 Message-Id: <20230327-pidfd-file-api-v1-1-5c0e9a3158e4@kernel.org> References: <20230327-pidfd-file-api-v1-0-5c0e9a3158e4@kernel.org> In-Reply-To: <20230327-pidfd-file-api-v1-0-5c0e9a3158e4@kernel.org> To: linux-fsdevel@vger.kernel.org Cc: Jan Kara , Amir Goldstein , Matthew Bobrowski , linux-kernel@vger.kernel.org, Christian Brauner X-Mailer: b4 0.13-dev-00303 X-Developer-Signature: v=1; a=openpgp-sha256; l=3959; i=brauner@kernel.org; h=from:subject:message-id; bh=fQqYYZBl6thY1SMZV6P0vcEwNdRfXWrP08DeYYxt4Z4=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMaQo3mcI5rrLdWapP9exJC/fi+w7D703fVQ7+eZc1mkeevNl TzZO7ChlYRDjYpAVU2RxaDcJl1vOU7HZKFMDZg4rE8gQBi5OAZiIVz/D/6r9W1Vcm3acMmSvOrYq9N /bILdeDQf+fINXzUt5wlVfv2Nk+Dxdy89Uh29dOOchWe+XOyY8mTcnVsvdjJVzujJD/5XLHAA= X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 X-Spam-Status: No, score=-5.2 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI,SPF_HELO_NONE, SPF_PASS autolearn=unavailable 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?1761546811955768399?= X-GMAIL-MSGID: =?utf-8?q?1761546811955768399?= Add a new helper that allows to reserve a pidfd and allocates a new pidfd file that stashes the provided struct pid. This will allow us to remove places that either open code this function or that call pidfd_create() but then have to call close_fd() because there are still failure points after pidfd_create() has been called. Signed-off-by: Christian Brauner Reviewed-by: Jan Kara --- include/linux/pid.h | 1 + kernel/pid.c | 69 +++++++++++++++++++++++++++++++++++++++++++---------- 2 files changed, 58 insertions(+), 12 deletions(-) diff --git a/include/linux/pid.h b/include/linux/pid.h index 343abf22092e..b75de288a8c2 100644 --- a/include/linux/pid.h +++ b/include/linux/pid.h @@ -80,6 +80,7 @@ extern struct pid *pidfd_pid(const struct file *file); struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags); struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags); int pidfd_create(struct pid *pid, unsigned int flags); +int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret); static inline struct pid *get_pid(struct pid *pid) { diff --git a/kernel/pid.c b/kernel/pid.c index 3fbc5e46b721..95e7e01574c8 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -576,6 +576,56 @@ struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags) return task; } +/** + * pidfd_prepare - allocate a new pidfd_file and reserve a pidfd + * @pid: the struct pid for which to create a pidfd + * @flags: flags of the new @pidfd + * @pidfd: the pidfd to return + * + * Allocate a new file that stashes @pid and reserve a new pidfd number in the + * caller's file descriptor table. The pidfd is reserved but not installed yet. + * + * If this function returns successfully the caller is responsible to either + * call fd_install() passing the returned pidfd and pidfd file as arguments in + * order to install the pidfd into its file descriptor table or they must use + * put_unused_fd() and fput() on the returned pidfd and pidfd file + * respectively. + * + * This function is useful when a pidfd must already be reserved but there + * might still be points of failure afterwards and the caller wants to ensure + * that no pidfd is leaked into its file descriptor table. + * + * Return: On success, a reserved pidfd is returned from the function and a new + * pidfd file is returned in the last argument to the function. On + * error, a negative error code is returned from the function and the + * last argument remains unchanged. + */ +int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret) +{ + int pidfd; + struct file *pidfd_file; + + if (!pid || !pid_has_task(pid, PIDTYPE_TGID)) + return -EINVAL; + + if (flags & ~(O_NONBLOCK | O_RDWR | O_CLOEXEC)) + return -EINVAL; + + pidfd = get_unused_fd_flags(O_RDWR | O_CLOEXEC); + if (pidfd < 0) + return pidfd; + + pidfd_file = anon_inode_getfile("[pidfd]", &pidfd_fops, pid, + flags | O_RDWR | O_CLOEXEC); + if (IS_ERR(pidfd_file)) { + put_unused_fd(pidfd); + return PTR_ERR(pidfd_file); + } + get_pid(pid); /* held by pidfd_file now */ + *ret = pidfd_file; + return pidfd; +} + /** * pidfd_create() - Create a new pid file descriptor. * @@ -594,20 +644,15 @@ struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags) */ int pidfd_create(struct pid *pid, unsigned int flags) { - int fd; + int pidfd; + struct file *pidfd_file; - if (!pid || !pid_has_task(pid, PIDTYPE_TGID)) - return -EINVAL; - - if (flags & ~(O_NONBLOCK | O_RDWR | O_CLOEXEC)) - return -EINVAL; - - fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid), - flags | O_RDWR | O_CLOEXEC); - if (fd < 0) - put_pid(pid); + pidfd = pidfd_prepare(pid, flags, &pidfd_file); + if (pidfd < 0) + return pidfd; - return fd; + fd_install(pidfd, pidfd_file); + return pidfd; } /**