From patchwork Wed Aug 28 03:03:14 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Yafang Shao X-Patchwork-Id: 13780370 X-Patchwork-Delegate: paul@paul-moore.com Received: from mail-pl1-f179.google.com (mail-pl1-f179.google.com [209.85.214.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A011C8BFC; Wed, 28 Aug 2024 03:03:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.179 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724814227; cv=none; b=GxZmKVDPMmGj/rmpwqdt5pvX0HsqkVx6E8FlSDR4g64erOO0/dNzjUJQV88PFEd4YeXlRk+t5TJqPJxWQaN8GeFM9ppFCA+XwaNc+qYopV6BSO/tN3zs4NiU+yB/mmPAVaDOpV8VM0b58MP9vSO+RFLFo77uxLgG2bqgRiSWdts= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724814227; c=relaxed/simple; bh=eO9Ix3cDnJp1QjWFcUiG7UEKoDBxWiAVcCPosvEyIKM=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=BxgVcqps7hac4NA9JyWNnvXuXPN/fRYWTdJC++qRvEXMvVlDzdRV5iNsh4xZbQnbffhiEAjRkGToNBmsDGY+jRd1587v4k0BMVz3dWd7GZWldyhXMnVAVM5HVbC8vJQbjmaS/7m1HdoAq4Gn29XU2C6w02AxwRn+dtfMxk3W4Hs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=MUBOuJ2i; arc=none smtp.client-ip=209.85.214.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="MUBOuJ2i" Received: by mail-pl1-f179.google.com with SMTP id d9443c01a7336-20223b5c1c0so56700165ad.2; Tue, 27 Aug 2024 20:03:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1724814225; x=1725419025; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=5dwC82d7KQL5pIEF6T6/bNHtBQAMogTq8DRZCJ210sw=; b=MUBOuJ2iO+3/ruxAgYLJpp5Lax6PhGENSOW8EZrQIxqWjCZXUYtAEpiBSzWneCdxEq wOHHjBgqEKhixXX1eU/5RqwniUnjWDBB5v1+6+HnIbIZTFWZP2SKrKeqQGleMNkRALOm IpAeTVjIcMEg1RLZjrSK3yEkwN5bBuJxo5uMpTSUTTwsDsZMiCspkCeBg/T59E0l3f3V yyZqi89MrCR1PEIW98XpCsK48J8vjTdHr3cTobd8CkLOs/IFta4pitILXl+JahVlPq8C d3NSH3liTy63UxzLTao0Sc57ghue6yeGij0RW2PQvCKLbG/+ufSkVcC7M9UO1vXZul+y IC8w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1724814225; x=1725419025; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=5dwC82d7KQL5pIEF6T6/bNHtBQAMogTq8DRZCJ210sw=; b=EUMJmlhpkIPvpqITsCqW4NhhSdmTlzeT6JVhqBqNX8qEUpTl6m9jXqDMNJTIT5sg4h W/1Z47evxf90vMgtNXHPCblldDTeOrRJk67/9k+YQDHK2eB6Qb7oZb+RFEUnufdaPCht aitPi1YBSgqEU5dQN1OWuSe+pYkZ4FWvgxHCLMTC9HJen+Eq5GOwF9mSk2Ry4OuoZvoY yx9rX+n0FnGxTobqgn0j0KS3gMfKqNVCA/Kek+ZGXTuk6aji1szGN8hyNiWh81bgsYSg e5GMamUTRzXDLcttYNLfQUsVPGdJkxwacKvFWr33Fw9r/vgXYs5I7RQXucz29W+DO0zn MeTw== X-Forwarded-Encrypted: i=1; AJvYcCV6BlohGvgC07xann8Q0ZwPqog5V9hAJr5zt+Axu5xG6APi3FJ1QZjc405Ec+jAKUJ3TnJU@vger.kernel.org, AJvYcCVHAsbnIV7AdlAvnRQewozktlP6O2pWjSlsZrFQ9GFEWFDehD1iTxMKs/KxkGBfB4JI6Y5f0rM7tsiQMZwchcmZZP8o@vger.kernel.org, AJvYcCWSeshAYNVMcbPzyXNSr+euxWfUJah1nqNV7rX1eOrU08qqdc5tXYT25pTQyVPVMEu8sbZ/rQ3LOg==@vger.kernel.org, AJvYcCWXLaNZclytA79b5YnAsBGLZO6VEGKdf/5n4eKhDIuEp6py51NbHA2P89iGgZhM1QFOCDubmA==@vger.kernel.org, AJvYcCWbERGOA9UlFVq1zasIVjhgGY4po8rCo3NctGH0dvknDlQovE99I2IaK3IKSQz/QuJFSPXX65CC@vger.kernel.org, AJvYcCX5Z3QwHOHCw9txstSVwQc7w+7vo4UH7mTPPRUEbxbiGBc4F88oDl21jELGlx8T1kqMRkvmJvPCkTePvDbu0bA/QMZCAjCT@vger.kernel.org, AJvYcCXilUq/Yb1ImwJlgRTtHc9L2BjZSaPM7ce1bVRSHS096/OwrKB3+y0Ur/vLR4VyB8Bf4ZXw3CeviMevgSccYw==@vger.kernel.org X-Gm-Message-State: AOJu0Yy1oZ10vU3dFrkSFZLjWweaVJobYB3PdrCM3iL9lHcoZ7/3hF/Q xL10bUwREH/XBB0IgLRnNIqzdMzBklYp4ULjgFRbzbrJYbHzrYLs X-Google-Smtp-Source: AGHT+IEc8gy1oBP9Tt27kWFVV2/sdUfpEnu0CJVUYvciPK7kLGNgdrFqezJmS8xsximWyUWY+TcSOg== X-Received: by 2002:a17:90a:d490:b0:2ca:7636:2217 with SMTP id 98e67ed59e1d1-2d8440a87edmr695434a91.2.1724814224691; Tue, 27 Aug 2024 20:03:44 -0700 (PDT) Received: from localhost.localdomain ([39.144.104.43]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2d8445db8f6sm317977a91.1.2024.08.27.20.03.36 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 27 Aug 2024 20:03:44 -0700 (PDT) From: Yafang Shao To: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org, alx@kernel.org, justinstitt@google.com, ebiederm@xmission.com, alexei.starovoitov@gmail.com, rostedt@goodmis.org, catalin.marinas@arm.com, penguin-kernel@i-love.sakura.ne.jp, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, audit@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org, dri-devel@lists.freedesktop.org, Yafang Shao , Alexander Viro , Christian Brauner , Jan Kara , Kees Cook , Matus Jokay , "Serge E. Hallyn" Subject: [PATCH v8 1/8] Get rid of __get_task_comm() Date: Wed, 28 Aug 2024 11:03:14 +0800 Message-Id: <20240828030321.20688-2-laoar.shao@gmail.com> X-Mailer: git-send-email 2.30.1 (Apple Git-130) In-Reply-To: <20240828030321.20688-1-laoar.shao@gmail.com> References: <20240828030321.20688-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: audit@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 We want to eliminate the use of __get_task_comm() for the following reasons: - The task_lock() is unnecessary Quoted from Linus [0]: : Since user space can randomly change their names anyway, using locking : was always wrong for readers (for writers it probably does make sense : to have some lock - although practically speaking nobody cares there : either, but at least for a writer some kind of race could have : long-term mixed results - The BUILD_BUG_ON() doesn't add any value The only requirement is to ensure that the destination buffer is a valid array. - Zeroing is not necessary in current use cases To avoid confusion, we should remove it. Moreover, not zeroing could potentially make it easier to uncover bugs. If the caller needs a zero-padded task name, it should be explicitly handled at the call site. Suggested-by: Linus Torvalds Link: https://lore.kernel.org/all/CAHk-=wivfrF0_zvf+oj6==Sh=-npJooP8chLPEfaFV0oNYTTBA@mail.gmail.com [0] Link: https://lore.kernel.org/all/CAHk-=whWtUC-AjmGJveAETKOMeMFSTwKwu99v7+b6AyHMmaDFA@mail.gmail.com/ Suggested-by: Alejandro Colomar Link: https://lore.kernel.org/all/2jxak5v6dfxlpbxhpm3ey7oup4g2lnr3ueurfbosf5wdo65dk4@srb3hsk72zwq Signed-off-by: Yafang Shao Cc: Alexander Viro Cc: Christian Brauner Cc: Jan Kara Cc: Eric Biederman Cc: Kees Cook Cc: Alexei Starovoitov Cc: Matus Jokay Cc: Alejandro Colomar Cc: "Serge E. Hallyn" --- fs/exec.c | 10 ---------- fs/proc/array.c | 2 +- include/linux/sched.h | 32 ++++++++++++++++++++++++++------ kernel/kthread.c | 2 +- 4 files changed, 28 insertions(+), 18 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 50e76cc633c4..8a23171bc3c3 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1264,16 +1264,6 @@ static int unshare_sighand(struct task_struct *me) return 0; } -char *__get_task_comm(char *buf, size_t buf_size, struct task_struct *tsk) -{ - task_lock(tsk); - /* Always NUL terminated and zero-padded */ - strscpy_pad(buf, tsk->comm, buf_size); - task_unlock(tsk); - return buf; -} -EXPORT_SYMBOL_GPL(__get_task_comm); - /* * These functions flushes out all traces of the currently running executable * so that a new one can be started diff --git a/fs/proc/array.c b/fs/proc/array.c index 34a47fb0c57f..55ed3510d2bb 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -109,7 +109,7 @@ void proc_task_name(struct seq_file *m, struct task_struct *p, bool escape) else if (p->flags & PF_KTHREAD) get_kthread_comm(tcomm, sizeof(tcomm), p); else - __get_task_comm(tcomm, sizeof(tcomm), p); + get_task_comm(tcomm, p); if (escape) seq_escape_str(m, tcomm, ESCAPE_SPACE | ESCAPE_SPECIAL, "\n\\"); diff --git a/include/linux/sched.h b/include/linux/sched.h index f8d150343d42..c40b95a79d80 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1096,9 +1096,12 @@ struct task_struct { /* * executable name, excluding path. * - * - normally initialized setup_new_exec() - * - access it with [gs]et_task_comm() - * - lock it with task_lock() + * - normally initialized begin_new_exec() + * - set it with set_task_comm() + * - strscpy_pad() to ensure it is always NUL-terminated and + * zero-padded + * - task_lock() to ensure the operation is atomic and the name is + * fully updated. */ char comm[TASK_COMM_LEN]; @@ -1914,10 +1917,27 @@ static inline void set_task_comm(struct task_struct *tsk, const char *from) __set_task_comm(tsk, from, false); } -extern char *__get_task_comm(char *to, size_t len, struct task_struct *tsk); +/* + * - Why not use task_lock()? + * User space can randomly change their names anyway, so locking for readers + * doesn't make sense. For writers, locking is probably necessary, as a race + * condition could lead to long-term mixed results. + * The strscpy_pad() in __set_task_comm() can ensure that the task comm is + * always NUL-terminated and zero-padded. Therefore the race condition between + * reader and writer is not an issue. + * + * - Why not use strscpy_pad()? + * While strscpy_pad() prevents writing garbage past the NUL terminator, which + * is useful when using the task name as a key in a hash map, most use cases + * don't require this. Zero-padding might confuse users if it’s unnecessary, + * and not zeroing might even make it easier to expose bugs. If you need a + * zero-padded task name, please handle that explicitly at the call site. + * + * - ARRAY_SIZE() can help ensure that @buf is indeed an array. + */ #define get_task_comm(buf, tsk) ({ \ - BUILD_BUG_ON(sizeof(buf) != TASK_COMM_LEN); \ - __get_task_comm(buf, sizeof(buf), tsk); \ + strscpy(buf, (tsk)->comm, ARRAY_SIZE(buf)); \ + buf; \ }) #ifdef CONFIG_SMP diff --git a/kernel/kthread.c b/kernel/kthread.c index f7be976ff88a..7d001d033cf9 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -101,7 +101,7 @@ void get_kthread_comm(char *buf, size_t buf_size, struct task_struct *tsk) struct kthread *kthread = to_kthread(tsk); if (!kthread || !kthread->full_name) { - __get_task_comm(buf, buf_size, tsk); + strscpy(buf, tsk->comm, buf_size); return; }