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AJvYcCX3IV7Yc6A51Vy1VsuK6PawnOx51ePaauJh1kzuQh7yymJqDwTKYu571AAK/wnYwvmE0Oy7K7SDBUfQMXdZFd8IXvbzcrUZ8qJpHCE/013/FJedEej8e1zhmwDxMiUBjjKl1bbbJ0TyLH1WBQ7vMl9/dAK71bkgi5QFtq7+/uVCsYyoUDek9/Rb17yHEYIOfWrFkNaZXwQuCGI9isBvlaVYjePi5QqtiKHFYPgfSP2vuAuS1OC3XsPr32hBT0T0O9dRNjH6BJBEsinJFc4rkDfpZUU2YYYqyqt6CiYFuUXicU1lyPidyV0RxT6n5N7t7vONcD9FPQ== X-Gm-Message-State: AOJu0YzvHvLmQDC+BBfjTpzDa0lrzlK+/rUBZ2qCSQ/IxVhEpMQ6Cmoi N/amvhN9KcHenFps5EcXOUR+emFeXuiEgU0G3osodaxhxNG8Geb0 X-Google-Smtp-Source: AGHT+IEUvSCxvTt2iFtiQZnOEMmTj53JiCANDbCPnBaNHXCCebMev5gTq4Ke5agmpYOP2sLQoQ29tA== X-Received: by 2002:a17:90b:3793:b0:2c9:5c7c:815d with SMTP id 98e67ed59e1d1-2cf7e2275d2mr4251165a91.22.1722220716985; Sun, 28 Jul 2024 19:38:36 -0700 (PDT) Received: from localhost.localdomain ([223.104.210.31]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2cf28c55a38sm7332247a91.10.2024.07.28.19.38.23 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sun, 28 Jul 2024 19:38:36 -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 , Alexander Viro , Christian Brauner , Jan Kara , Kees Cook , Matus Jokay Subject: [PATCH v4 01/11] fs/exec: Drop task_lock() inside __get_task_comm() Date: Mon, 29 Jul 2024 10:37:09 +0800 Message-Id: <20240729023719.1933-2-laoar.shao@gmail.com> X-Mailer: git-send-email 2.30.1 (Apple Git-130) In-Reply-To: <20240729023719.1933-1-laoar.shao@gmail.com> References: <20240729023719.1933-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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] 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 --- fs/exec.c | 10 ++++++++-- include/linux/sched.h | 4 ++-- 2 files changed, 10 insertions(+), 4 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 40073142288f..fa6b61c79df8 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1238,12 +1238,18 @@ static int unshare_sighand(struct task_struct *me) return 0; } +/* + * 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. + */ 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); diff --git a/include/linux/sched.h b/include/linux/sched.h index 61591ac6eab6..95888d1da49e 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1086,9 +1086,9 @@ struct task_struct { /* * executable name, excluding path. * - * - normally initialized setup_new_exec() + * - normally initialized begin_new_exec() * - access it with [gs]et_task_comm() - * - lock it with task_lock() + * - lock it with task_lock() for writing */ char comm[TASK_COMM_LEN];