linux-kernel - [PATCH RFC 1/4] pidfs: register pid in pidfs

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 for Android: free password hash cracker in your pocket

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

Message-Id: <20250424-work-pidfs-net-v1-1-0dc97227d854@kernel.org>
Date: Thu, 24 Apr 2025 14:24:34 +0200
From: Christian Brauner <brauner@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>, Kuniyuki Iwashima <kuniyu@...zon.com>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
 netdev@...r.kernel.org, David Rheinsberg <david@...dahead.eu>, 
 Jan Kara <jack@...e.cz>, Alexander Mikhalitsyn <alexander@...alicyn.com>, 
 Luca Boccassi <bluca@...ian.org>, 
 Lennart Poettering <lennart@...ttering.net>, 
 Daan De Meyer <daan.j.demeyer@...il.com>, Mike Yuan <me@...dnzj.com>, 
 Christian Brauner <brauner@...nel.org>
Subject: [PATCH RFC 1/4] pidfs: register pid in pidfs

Add simple helpers that allow a struct pid to be pinned via a pidfs
dentry/inode. If no pidfs dentry exists a new one will be allocated for
it. A reference is taken by pidfs on @pid. The reference must be
released via pidfs_put_pid().

This will allow AF_UNIX sockets to allocate a dentry for the peer
credentials pid at the time they are recorded where we know the task is
still alive. When the task gets reaped its exit status is guaranteed to
be recorded and a pidfd can be handed for the reaped task.

Signed-off-by: Christian Brauner <brauner@...nel.org>
---
 fs/pidfs.c            | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pidfs.h |  3 +++
 2 files changed, 61 insertions(+)

diff --git a/fs/pidfs.c b/fs/pidfs.c
index d64a4cbeb0da..8e6c11774c60 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -896,6 +896,64 @@ struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
 	return pidfd_file;
 }

+/**
+ * pidfs_register_pid - pin a struct pid through pidfs
+ * @pid: pid to pin
+ *
+ * Pin a struct pid through pidfs. Needs to be paired with
+ * pidfds_put_put() to not risk leaking the pidfs dentry and inode.
+ *
+ * Return: On success zero, on error a negative error code is returned.
+ */
+int pidfs_register_pid(struct pid *pid)
+{
+	struct path path __free(path_put) = {};
+	int ret;
+
+	might_sleep();
+
+	if (!pid)
+		return 0;
+
+	ret = path_from_stashed(&pid->stashed, pidfs_mnt, get_pid(pid), &path);
+	if (unlikely(ret))
+		return ret;
+	path.dentry = NULL;
+	return 0;
+}
+
+/**
+ * pidfs_get_pid - pin a struct pid through pidfs
+ * @pid: pid to pin
+ *
+ * Similar to pidfs_register_pid() but only valid if the caller knows
+ * there's a reference to the @pid through its dentry already.
+ */
+void pidfs_get_pid(struct pid *pid)
+{
+	if (!pid)
+		return;
+
+	WARN_ON_ONCE(stashed_dentry_get(&pid->stashed) == NULL);
+}
+
+/**
+ * pidfs_put_pid - drop a pidfs reference
+ * @pid: pid to drop
+ *
+ * Drop a reference to @pid via pidfs. This is only safe if the
+ * reference has been taken via pidfs_get_pid().
+ */
+void pidfs_put_pid(struct pid *pid)
+{
+	might_sleep();
+
+	if (!pid)
+		return;
+
+	dput(pid->stashed);
+}
+
 static void pidfs_inode_init_once(void *data)
 {
 	struct pidfs_inode *pi = data;
diff --git a/include/linux/pidfs.h b/include/linux/pidfs.h
index 05e6f8f4a026..2676890c4d0d 100644
--- a/include/linux/pidfs.h
+++ b/include/linux/pidfs.h
@@ -8,5 +8,8 @@ void pidfs_add_pid(struct pid *pid);
 void pidfs_remove_pid(struct pid *pid);
 void pidfs_exit(struct task_struct *tsk);
 extern const struct dentry_operations pidfs_dentry_operations;
+int pidfs_register_pid(struct pid *pid);
+void pidfs_get_pid(struct pid *pid);
+void pidfs_put_pid(struct pid *pid);

 #endif /* _LINUX_PID_FS_H */

-- 
2.47.2