From patchwork Mon May 16 21:19:15 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Stultz X-Patchwork-Id: 1505 Return-Path: Delivered-To: unknown Received: from imap.gmail.com (74.125.159.109) by localhost6.localdomain6 with IMAP4-SSL; 08 Jun 2011 14:52:34 -0000 Delivered-To: patches@linaro.org Received: by 10.224.61.3 with SMTP id r3cs96503qah; Mon, 16 May 2011 14:19:26 -0700 (PDT) Received: by 10.151.92.10 with SMTP id u10mr4001858ybl.72.1305580766446; Mon, 16 May 2011 14:19:26 -0700 (PDT) Received: from e38.co.us.ibm.com (e38.co.us.ibm.com [32.97.110.159]) by mx.google.com with ESMTPS id u16si12311471yba.2.2011.05.16.14.19.25 (version=TLSv1/SSLv3 cipher=OTHER); Mon, 16 May 2011 14:19:25 -0700 (PDT) Received-SPF: pass (google.com: domain of jstultz@us.ibm.com designates 32.97.110.159 as permitted sender) client-ip=32.97.110.159; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jstultz@us.ibm.com designates 32.97.110.159 as permitted sender) smtp.mail=jstultz@us.ibm.com Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e38.co.us.ibm.com (8.14.4/8.13.1) with ESMTP id p4GLBKel019918; Mon, 16 May 2011 15:11:20 -0600 Received: from d03av02.boulder.ibm.com (d03av02.boulder.ibm.com [9.17.195.168]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id p4GLJMJl090620; Mon, 16 May 2011 15:19:22 -0600 Received: from d03av02.boulder.ibm.com (loopback [127.0.0.1]) by d03av02.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p4GFIrGM004566; Mon, 16 May 2011 09:18:54 -0600 Received: from kernel.beaverton.ibm.com (kernel.beaverton.ibm.com [9.47.67.96]) by d03av02.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id p4GFIquZ004531; Mon, 16 May 2011 09:18:52 -0600 Received: by kernel.beaverton.ibm.com (Postfix, from userid 1056) id 20B191E750D; Mon, 16 May 2011 14:19:19 -0700 (PDT) From: John Stultz To: LKML Cc: John Stultz , "Ted Ts'o" , KOSAKI Motohiro , David Rientjes , Dave Hansen , Andrew Morton , linux-mm@kvack.org Subject: [PATCH 1/3] comm: Introduce comm_lock seqlock to protect task->comm access Date: Mon, 16 May 2011 14:19:15 -0700 Message-Id: <1305580757-13175-2-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 1.7.3.2.146.gca209 In-Reply-To: <1305580757-13175-1-git-send-email-john.stultz@linaro.org> References: <1305580757-13175-1-git-send-email-john.stultz@linaro.org> The implicit rules for current->comm access being safe without locking are no longer true. Accessing current->comm without holding the task lock may result in null or incomplete strings (however, access won't run off the end of the string). In order to properly fix this, I've introduced a comm_lock spinlock which will protect comm access and modified get_task_comm() and set_task_comm() to use it. Since there are a number of cases where comm access is open-coded safely grabbing the task_lock(), we preserve the task locking in set_task_comm, so those users are also safe. With this patch, users that access current->comm without a lock are still prone to null/incomplete comm strings, but it should be no worse then it is now. The next step is to go through and convert all comm accesses to use get_task_comm(). This is substantial, but can be done bit by bit, reducing the race windows with each patch. CC: Ted Ts'o CC: KOSAKI Motohiro CC: David Rientjes CC: Dave Hansen CC: Andrew Morton CC: linux-mm@kvack.org Acked-by: David Rientjes Signed-off-by: John Stultz --- fs/exec.c | 19 ++++++++++++++++--- include/linux/init_task.h | 1 + include/linux/sched.h | 5 ++--- 3 files changed, 19 insertions(+), 6 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 5e62d26..34fa611 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -998,17 +998,28 @@ static void flush_old_files(struct files_struct * files) char *get_task_comm(char *buf, struct task_struct *tsk) { - /* buf must be at least sizeof(tsk->comm) in size */ - task_lock(tsk); + unsigned long flags; + + spin_lock_irqsave(&tsk->comm_lock, flags); strncpy(buf, tsk->comm, sizeof(tsk->comm)); - task_unlock(tsk); + spin_unlock_irqrestore(&tsk->comm_lock, flags); return buf; } void set_task_comm(struct task_struct *tsk, char *buf) { + unsigned long flags; + + /* + * XXX - Even though comm is protected by comm_lock, + * we take the task_lock here to serialize against + * current users that directly access comm. + * Once those users are removed, we can drop the + * task locking & memsetting. + */ task_lock(tsk); + spin_lock_irqsave(&tsk->comm_lock, flags); /* * Threads may access current->comm without holding * the task lock, so write the string carefully. @@ -1018,6 +1029,8 @@ void set_task_comm(struct task_struct *tsk, char *buf) memset(tsk->comm, 0, TASK_COMM_LEN); wmb(); strlcpy(tsk->comm, buf, sizeof(tsk->comm)); + spin_unlock_irqrestore(&tsk->comm_lock, flags); + task_unlock(tsk); perf_event_comm(tsk); } diff --git a/include/linux/init_task.h b/include/linux/init_task.h index caa151f..b69d94b 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -161,6 +161,7 @@ extern struct cred init_cred; .group_leader = &tsk, \ RCU_INIT_POINTER(.real_cred, &init_cred), \ RCU_INIT_POINTER(.cred, &init_cred), \ + .comm_lock = __SPIN_LOCK_UNLOCKED(tsk.comm_lock), \ .comm = "swapper", \ .thread = INIT_THREAD, \ .fs = &init_fs, \ diff --git a/include/linux/sched.h b/include/linux/sched.h index 18d63ce..f8a7cdf 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1333,10 +1333,9 @@ struct task_struct { const struct cred __rcu *cred; /* effective (overridable) subjective task * credentials (COW) */ struct cred *replacement_session_keyring; /* for KEYCTL_SESSION_TO_PARENT */ - + spinlock_t comm_lock; /* protect's comm */ char comm[TASK_COMM_LEN]; /* executable name excluding path - - access with [gs]et_task_comm (which lock - it with task_lock()) + - access with [gs]et_task_comm - initialized normally by setup_new_exec */ /* file system info */ int link_count, total_link_count;