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AJvYcCXKtglx9LHY+w6U/mNzIeT3qmIMrVvSzwprlE5E5+8p9/ax920mziZHkh9uJVMd7Qwd2Xfo9kmNaFX/YlD8IDrJ3+Ccl+7Z3gFfqwpfmeDQmZkUlL83CMJJQZs+wFS64RgRdM6+3JEu6IbmnkkAUtuFhq5R1nysMjhOMvoKUGKXyDEdCbuQxeCCoFDbQWz6tBRIE1aC9XmnbZ5vl55iIs+89K1ttwBaz/MFWeQuD3Y8v104ivJCshWfLQdY+Tn4926sPUd516K7Fkn0COmmLljJ3ZlrKxs8xZo0pBdwnseurk6AyERFjQA8dtkJn78m2FyLSEEXBw== X-Gm-Message-State: AOJu0Yxu6xT+mfXekcJIm3o3xJ+81vVAhOh7BdwEk33o5+PYMpyc6oVz at3FGkIZrpS6mGJNwtNXqMwNMYq/ithrxnPs+eQGNwVdaqxxZ36Z X-Google-Smtp-Source: AGHT+IGepHvi+lKqMo1GYaife0L6fUJVRPiktMyHkXeHwR+7tr6qOJAeLHRN5Lin69VRxAqus5DeJQ== X-Received: by 2002:a17:902:ecc1:b0:1f6:6ef0:dae4 with SMTP id d9443c01a7336-1f83b5f3fffmr43616545ad.32.1718245871101; Wed, 12 Jun 2024 19:31:11 -0700 (PDT) Received: from localhost.localdomain ([39.144.105.92]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1f855f4d159sm1755695ad.289.2024.06.12.19.31.03 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 12 Jun 2024 19:31:10 -0700 (PDT) From: Yafang Shao To: torvalds@linux-foundation.org Cc: ebiederm@xmission.com, alexei.starovoitov@gmail.com, rostedt@goodmis.org, 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 v2 01/10] fs/exec: Drop task_lock() inside __get_task_comm() Date: Thu, 13 Jun 2024 10:30:35 +0800 Message-Id: <20240613023044.45873-2-laoar.shao@gmail.com> X-Mailer: git-send-email 2.30.1 (Apple Git-130) In-Reply-To: <20240613023044.45873-1-laoar.shao@gmail.com> References: <20240613023044.45873-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: bpf@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];