linux-kernel - [PATCH v2 1/2] pid: add pidfd_get

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20211011133245.1703103-2-brauner@kernel.org>
Date:   Mon, 11 Oct 2021 15:32:44 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Matthew Bobrowski <repnop@...gle.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>, Jan Kara <jack@...e.cz>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Minchan Kim <minchan@...nel.org>
Subject: [PATCH v2 1/2] pid: add pidfd_get_task() helper

From: Christian Brauner <christian.brauner@...ntu.com>

The number of system calls making use of pidfds is constantly
increasing. Some of those new system calls duplicate the code to turn a
pidfd into task_struct it refers to. Give them a simple helper for this.

Link: https://lore.kernel.org/r/20211004125050.1153693-2-christian.brauner@ubuntu.com
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Cc: Matthew Bobrowski <repnop@...gle.com>
Cc: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: Jan Kara <jack@...e.cz>
Cc: Minchan Kim <minchan@...nel.org>
Reviewed-by: Matthew Bobrowski <repnop@...gle.com>
Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
/* v2 */
- David Hildenbrand <david@...hat.com>:
  - Also document that the caller is expected to decrease the reference
    count on the returned task.
---
 include/linux/pid.h |  1 +
 kernel/pid.c        | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/include/linux/pid.h b/include/linux/pid.h
index af308e15f174..343abf22092e 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -78,6 +78,7 @@ struct file;
 
 extern struct pid *pidfd_pid(const struct file *file);
 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
+struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
 int pidfd_create(struct pid *pid, unsigned int flags);
 
 static inline struct pid *get_pid(struct pid *pid)
diff --git a/kernel/pid.c b/kernel/pid.c
index efe87db44683..2fc0a16ec77b 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -539,6 +539,42 @@ struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags)
 	return pid;
 }
 
+/**
+ * pidfd_get_task() - Get the task associated with a pidfd
+ *
+ * @pidfd: pidfd for which to get the task
+ * @flags: flags associated with this pidfd
+ *
+ * Return the task associated with @pidfd. The function takes a reference on
+ * the returned task. The caller is responsible for releasing that reference.
+ *
+ * Currently, the process identified by @pidfd is always a thread-group leader.
+ * This restriction currently exists for all aspects of pidfds including pidfd
+ * creation (CLONE_PIDFD cannot be used with CLONE_THREAD) and pidfd polling
+ * (only supports thread group leaders).
+ *
+ * Return: On success, the task_struct associated with the pidfd.
+ *	   On error, a negative errno number will be returned.
+ */
+struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags)
+{
+	unsigned int f_flags;
+	struct pid *pid;
+	struct task_struct *task;
+
+	pid = pidfd_get_pid(pidfd, &f_flags);
+	if (IS_ERR(pid))
+		return ERR_CAST(pid);
+
+	task = get_pid_task(pid, PIDTYPE_TGID);
+	put_pid(pid);
+	if (!task)
+		return ERR_PTR(-ESRCH);
+
+	*flags = f_flags;
+	return task;
+}
+
 /**
  * pidfd_create() - Create a new pid file descriptor.
  *
-- 
2.30.2