linux-kernel - [PATCH bpf-next 1/4] kernfs: Add __kernfs_xattr

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: <20250618233739.189106-2-song@kernel.org>
Date: Wed, 18 Jun 2025 16:37:36 -0700
From: Song Liu <song@...nel.org>
To: bpf@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Cc: kernel-team@...a.com,
	andrii@...nel.org,
	eddyz87@...il.com,
	ast@...nel.org,
	daniel@...earbox.net,
	martin.lau@...ux.dev,
	viro@...iv.linux.org.uk,
	brauner@...nel.org,
	jack@...e.cz,
	kpsingh@...nel.org,
	mattbobrowski@...gle.com,
	amir73il@...il.com,
	gregkh@...uxfoundation.org,
	tj@...nel.org,
	daan.j.demeyer@...il.com,
	Song Liu <song@...nel.org>
Subject: [PATCH bpf-next 1/4] kernfs: Add __kernfs_xattr_get for RCU protected access

Existing kernfs_xattr_get() locks iattr_mutex, so it cannot be used in
RCU critical sections. Introduce __kernfs_xattr_get(), which reads xattr
under RCU read lock. This can be used by BPF programs to access cgroupfs
xattrs.

Signed-off-by: Song Liu <song@...nel.org>
---
 fs/kernfs/inode.c      | 14 ++++++++++++++
 include/linux/kernfs.h |  2 ++
 2 files changed, 16 insertions(+)

diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index b83054da68b3..0ca231d2012c 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -302,6 +302,20 @@ int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
 	return simple_xattr_get(&attrs->xattrs, name, value, size);
 }
 
+int __kernfs_xattr_get(struct kernfs_node *kn, const char *name,
+		       void *value, size_t size)
+{
+	struct kernfs_iattrs *attrs;
+
+	WARN_ON_ONCE(!rcu_read_lock_held());
+
+	attrs = rcu_dereference(kn->iattr);
+	if (!attrs)
+		return -ENODATA;
+
+	return simple_xattr_get(&attrs->xattrs, name, value, size);
+}
+
 int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
 		     const void *value, size_t size, int flags)
 {
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index b5a5f32fdfd1..8536ffc5c9f1 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -456,6 +456,8 @@ void kernfs_notify(struct kernfs_node *kn);
 
 int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
 		     void *value, size_t size);
+int __kernfs_xattr_get(struct kernfs_node *kn, const char *name,
+		       void *value, size_t size);
 int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
 		     const void *value, size_t size, int flags);
 
-- 
2.47.1