From patchwork Mon Oct 7 14:49:05 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yafang Shao X-Patchwork-Id: 13824807 X-Patchwork-Delegate: rostedt@goodmis.org Received: from mail-pf1-f177.google.com (mail-pf1-f177.google.com [209.85.210.177]) (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 9D3521D416B; Mon, 7 Oct 2024 14:49:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.177 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728312587; cv=none; b=CGnYxb47i6nYsaDBr95Z/k2F2I+yT+f+bZjDEOGUySL53hIa8h2LStlhhuoPy407nCSZ8KeyYy9xZ4pQkQfB0nFtrQejTad0Q184iWTOmESvPCeZ5LWqwM2x5pqU+vGAuHyC5o9ViBxO2ehgdaNtbJVYI+fuzhyiLrGezHd5bGU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728312587; c=relaxed/simple; bh=LdUzXXQ8w1cxGk6eZCeHPTjeQKYbvyuMc5IN1L2pmJk=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=AeU9+altLSeXwZWE7UrUArURfQiy+g3xrfr9eE/0BCjquCLRIo5ls1xusx2DlcpF/5owqARXC2TsFaSNrDe8ufPDT2oTmMTyPyuabZ00i2uR57VZ0f4TwvfNevqYqxb5LHYxl1qv75CXtregUyWWPFnTTXJ0moInf6ARt+Wb3T0= 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=GlzFkGkc; arc=none smtp.client-ip=209.85.210.177 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="GlzFkGkc" Received: by mail-pf1-f177.google.com with SMTP id d2e1a72fcca58-71e02249621so748973b3a.1; Mon, 07 Oct 2024 07:49:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1728312585; x=1728917385; 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=oVEk6SmaURyo42RvRGYBr53delaAcBEjfSHuuD+Cst4=; b=GlzFkGkcVK0yU5uGVoyoDHvqoGswNz3QeNvFmV9+B3ta2Z1Fe1+Zz37tMI8E+btu93 DOq1Vakzmk57N7fk8V5TIFfEUAhrTqvTURA4yofAFzm9sdhi+czR7WfEX3uFHKgpaEE/ SNzKSoE7CiRsZqD9CI0x7UoiI9AW2al0WfHhfhu6/kRAjZo+UrtX65ThklzWpQ0cM9u6 QnlOePALakfWc8J4z4toK5JmfCPbyq4rNk7I7OyFiGMOaI4jgbykZ8LBUoHECXAKmmc2 AdWit+UniSXgsdXKkdNoqF0Zlw4PpwJc9SLwjgok1FK4hYmrsLZoe2pFrU2T8bs+8spT R9HA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1728312585; x=1728917385; 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=oVEk6SmaURyo42RvRGYBr53delaAcBEjfSHuuD+Cst4=; b=qjeZ67pqOXMAFwIH/H0ejCayzJshrT1bo97wIbvGY8n4J5JmsyMMFiq4VvGgjctKor TQdNLwja3Gas8YVlBzZOu7V699Tu1FYyugmTnt/HNz4RdryB0GO1nqXgsWG2dJu35740 1+0ZQflmYzIErH1Dacc8HpWgw2Bx8+rAhRPxbZs66QQ9PKaz+40QDDo6WnlmfXI2lG96 WYZ0Id0lNis9Ivp/G0TcOt+80fU4oUI7YaLllBJrZotpj4Ec/JljTtJ5RXod6MPco8m5 jEssgLl00DOuSu7Zv6bNvoJSbpz0DOpe93+mE7YuXUG0l4KIktIyleXnc61iSVNnZkE7 9KTA== X-Forwarded-Encrypted: i=1; AJvYcCU40V3TXsQNomPZeLtiq9By+KEviFuxVA7SgADQRK/pNC1vEzJ00K7iLzufzT7w1JvMd55N5rwTCRH5mSUXAzovJhpMdsY3@vger.kernel.org, AJvYcCUGx+b/xyJviZs7HkGNd6jUUMd7Tf7lFeDDdeMpHrgQgyJneyACzxq5RRKLQZi+ACvcKAz9@vger.kernel.org, AJvYcCWkfeIIwON9j1Ce7nKBs7IcG/avYjB1UvMj8N0igbgvebs00PfAOM9Q4peo1/+f0+fSHsghBs+YDgw+m7E93A==@vger.kernel.org, AJvYcCWn18yoLF+XeR7AW6Z5agDT9NR9Ii8AyNGaiDEYhThGQPoVP9u87wzGspwoPtwhPWiYnT6cvg==@vger.kernel.org, AJvYcCWnZCkJpzx4BDePSfxTgIYdCDCqCAtscIv5oTRqn1g65CAxnPRUUiovSMgCmd87WRI00CbQwJyZLvbOqutpzLyq5vP4@vger.kernel.org, AJvYcCXBlwPJUNoBgBWB2LAGgNQcJZP6wkwhPTdSDJXud4Zy/za7caMTENgOrRCHUD0MTcmWdUNeBPnU@vger.kernel.org, AJvYcCXhF6Ge+2BIA3epeq0nZHC6Whf2OHn1VZohsBPQwxcM3Kh6L5+ufmHnHuEXnHHfXCuvSTZ4MEfimQ==@vger.kernel.org X-Gm-Message-State: AOJu0YxYRNZG63PwcQoPl2H7AD6ylqC/X8vhQryWD/y+d7PNS3RJavzd utnb0PIKzI7zjroTPppZACsyylQXp2H+rG6VIitIc50VKPxotSAO X-Google-Smtp-Source: AGHT+IFysx44ym7xeNZ29ZQx56P8LK073YLR3FEq6ZYjPgOvQStiRImQUgMUmAdR1iJQTcm5/XW64g== X-Received: by 2002:a05:6a00:2eaa:b0:718:e162:7374 with SMTP id d2e1a72fcca58-71de239f5e6mr18318586b3a.5.1728312584814; Mon, 07 Oct 2024 07:49:44 -0700 (PDT) Received: from localhost.localdomain ([223.104.210.43]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-71df0d7cf82sm4466432b3a.200.2024.10.07.07.49.32 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 07 Oct 2024 07:49:44 -0700 (PDT) From: Yafang Shao To: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org, keescook@chromium.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 , Matus Jokay , "Serge E. Hallyn" Subject: [PATCH v9 1/7] Get rid of __get_task_comm() Date: Mon, 7 Oct 2024 22:49:05 +0800 Message-Id: <20241007144911.27693-2-laoar.shao@gmail.com> X-Mailer: git-send-email 2.30.1 (Apple Git-130) In-Reply-To: <20241007144911.27693-1-laoar.shao@gmail.com> References: <20241007144911.27693-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@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 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/ 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 | 28 ++++++++++++++++++++++------ kernel/kthread.c | 2 +- 4 files changed, 24 insertions(+), 18 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 6c53920795c2..77364806b48d 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1189,16 +1189,6 @@ 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 e6ee4258169a..28f92c637abf 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1121,9 +1121,12 @@ 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]; @@ -1938,10 +1941,23 @@ 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. + * + * - BUILD_BUG_ON() can help prevent the buf from being truncated. + * Since the callers don't perform any return value checks, this safeguard is + * necessary. + */ #define get_task_comm(buf, tsk) ({ \ - BUILD_BUG_ON(sizeof(buf) != TASK_COMM_LEN); \ - __get_task_comm(buf, sizeof(buf), tsk); \ + BUILD_BUG_ON(sizeof(buf) < TASK_COMM_LEN); \ + strscpy_pad(buf, (tsk)->comm); \ + buf; \ }) #ifdef CONFIG_SMP diff --git a/kernel/kthread.c b/kernel/kthread.c index db4ceb0f503c..74d20f46fa30 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; }