From patchwork Mon Aug 12 02:29:25 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Yafang Shao X-Patchwork-Id: 13759999 Received: from mail-pg1-f180.google.com (mail-pg1-f180.google.com [209.85.215.180]) (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 346A881E; Mon, 12 Aug 2024 02:30:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.180 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723429838; cv=none; b=A7WJH9MEmODJn2OWO6aqR7WAJjQpjpXtzVdBhEf2FVfkgfugHinZYqHLaep3pQ6NuJq9r84hFG5nnatI61jZWdu1sFAXhQ9q+AStIQnEmFHfq9zmsZZEu6aNvbQX9ua65Cgx96nlbkdq0p31/jDPChFfIbQ8DC/OawBcNhBag4s= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723429838; c=relaxed/simple; bh=OtCu8tCLyJLMIEL9JGTrh8+dXoRUm59kHwmUusfOtKw=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=Z57MeeZ04yDL3JPyVaHBRRipd8dOdYLtSVABZswWCZs0XF4xDtyp8phkgrDH3mOsEHY4D2JXTN7ZCSzX15yo/X4RF9leWgRx09xN9Gc9HkH96qKlrcLIgR1/NJ0dwWc4EIro0mm+Sg9mw0lVxvjyB//lT5XuF2G9i0HEjzaAxtw= 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=Zcq78NXS; arc=none smtp.client-ip=209.85.215.180 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="Zcq78NXS" Received: by mail-pg1-f180.google.com with SMTP id 41be03b00d2f7-7bb75419123so2512622a12.3; Sun, 11 Aug 2024 19:30:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1723429836; x=1724034636; 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=khhjXbPZMt7GBHDJwocHjgjVouiC9Zx1GPF6Kpp8feU=; b=Zcq78NXSk3Y2x0tkF4TVF5oppcstgDdsM1XcvIPwG5kr2OiUyNa7FKraXpdEPgSisO 0wsI/sSVJeBHLD4nENE5Ci65L4YomaUkJ2vY69aTQL5jx+mPVbJlzd9QFExczl7lfEuk tggcZ930r5EPDk625vS/Gbru+c8obwW/R2LKjvuAcJD27r/jShx455hCfvLVa92eQON7 1/iug/sq1k+aPZe3jPBOJXWr8JNC0EoLk91LdOHkznqpYfG23PyxEleyh2/zhAyYo4KN 2wekbOXrWpI5QTmayoAkIqzFMm6lsAONOW7VxvMqLqXblWZ+rNeeqqZImw0VYh3N+z9e 25SA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1723429836; x=1724034636; 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=khhjXbPZMt7GBHDJwocHjgjVouiC9Zx1GPF6Kpp8feU=; b=Mbgxc2iinTdP0OCnni3nkIz3Cc8SLRcZWTvjAb1io+ibR2OEtO3aIljZjtpQaFVoR/ UI+CJCO8t4N8MBtfncKrLmIQTUBK5ZxtIa2kYOb8fRYxCFwv/0gs7L9bq8DBxQIr9M0G UfqkN0kpJTGUHUUU9WfOfaVglwXmhIUPIe864GtosNmOEPkxOHpFUdAS9lZ9FZiKmR+c 4nzdR2Yyz6P5HOPK/7LvXLuWGTnsQGZloZEShRRLdXFErXAYN+G1fzl5CPfn4/CN3FEe hftcfvpwTBlcUIXSfb3CA7VtIMwAj6LX7HJnQr7axEces7crlizZg4ujYimDQoxD9DPq Y5aA== X-Forwarded-Encrypted: i=1; AJvYcCVlwaF7NxQAqjTC+U2nP+hYwP2Tw6VO+MZGJeTbWF39jplsek8lXfmC6wZbAJysQtqu5JKj5yv73Z6SFFxHgBPyTe65WdI1boeO5syEjJfuj15qQ7EjIn130W58dpBHIlG7EOOHcX7Hl+vyb0ixFRUbN+Vc1QJ/xXWJbz4UJZm6Ry6CmafUgkn/Igt2BileMgx1zuPYo8XDUrdaDJ5dPVqaAppFDrsxNjt9kQrfwknpxYE7Selhk0V+bzkp4cWHpl4PRTL8DZR1yjpEdpRdW5npGOlXA2eFAeFchWG9LyN6ejE5EsTvLMV94Ond8da3qMuXv7nqKA== X-Gm-Message-State: AOJu0Yzmf1LMm702JKGqwUP4PQCu38LHUM8UuGvN/RangnnJGGoHK5/0 SHwOU/yr4MAHPCdXUMHHe5IsKdb0oqA+RmynoJXD0tp6D++MTLdi X-Google-Smtp-Source: AGHT+IHZ0gPVVBMqlR8AM+LuQyCNFAmVaej1h0WqXQaGCWBBgBWQLJgV4NwTDuyMDp98EgrIiW/RCQ== X-Received: by 2002:a17:902:ce83:b0:1fb:3474:9500 with SMTP id d9443c01a7336-200ae56b418mr67022635ad.27.1723429836312; Sun, 11 Aug 2024 19:30:36 -0700 (PDT) Received: from localhost.localdomain ([39.144.39.162]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-200bb9fed69sm27884765ad.188.2024.08.11.19.30.04 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sun, 11 Aug 2024 19:30:35 -0700 (PDT) From: Yafang Shao To: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org, 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 , Alejandro Colomar , Alexander Viro , Christian Brauner , Jan Kara , Kees Cook , Matus Jokay , "Serge E. Hallyn" Subject: [PATCH v6 1/9] Get rid of __get_task_comm() Date: Mon, 12 Aug 2024 10:29:25 +0800 Message-Id: <20240812022933.69850-2-laoar.shao@gmail.com> X-Mailer: git-send-email 2.30.1 (Apple Git-130) In-Reply-To: <20240812022933.69850-1-laoar.shao@gmail.com> References: <20240812022933.69850-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: bpf@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 | 31 +++++++++++++++++++++++++------ kernel/kthread.c | 2 +- 4 files changed, 27 insertions(+), 18 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index a47d0e4c54f6..2e468ddd203a 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 33dd8d9d2b85..e0e26edbda61 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1096,9 +1096,11 @@ 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 + * - task_lock() to ensure the operation is atomic and the name is + * fully updated. */ char comm[TASK_COMM_LEN]; @@ -1912,10 +1914,27 @@ 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. 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; }