Merge tag 'vfs-7.3-rc1.kfunc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull vfs bpf access updates from Christian Brauner:
 "This adds a bpf_sock_read_xattr() kfunc so a BPF LSM program can read
  a user.* extended attribute from a socket's sockfs inode locklessly.

  userspace already uses user.* xattrs on sockets to implement socket
  rate limiting and to tag sockets for other purposes such as a varlink
  registry. There has been no efficient way for a BPF program to read
  those labels back. With this a listening socket marked from userspace
  with fsetxattr() can be read back during bind or connect and acted
  upon on the connecting socket. That lets userspace mark sockets and
  later rediscover them or implement policy on them"

* tag 'vfs-7.3-rc1.kfunc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  selftests/bpf: Add test for bpf_sock_read_xattr() kfunc
  fs: Add bpf_sock_read_xattr() kfunc to read socket xattrs

1 files changed, 25 insertions, 0 deletions

diff --git a/net/socket.c b/net/socket.c
index 63c69a0fa74e..b0256cd222f8 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -465,6 +465,31 @@ static const struct xattr_handler sockfs_user_xattr_handler = {
 	.set = sockfs_user_xattr_set,
 };
 
+/**
+ * sock_read_xattr - read a user.* xattr from a socket's sockfs inode
+ * @sock: socket whose inode holds the xattr
+ * @name: full xattr name, e.g. "user.bpf_test"
+ * @value: output buffer
+ * @size: size of @value in bytes
+ *
+ * SOCK_INODE() is valid only for sockfs sockets; sock_from_file() rejects
+ * anything else (e.g. tun, tap).
+ * Lockless: simple_xattr_get() looks up the value under RCU, no inode lock.
+ *
+ * Return: length of the value on success, a negative errno on error.
+ */
+int sock_read_xattr(struct socket *sock, const char *name, void *value, size_t size)
+{
+	struct file *file = sock->file;
+	struct sockfs_inode *si;
+
+	if (!file || sock_from_file(file) != sock)
+		return -EOPNOTSUPP;
+
+	si = SOCKFS_I(SOCK_INODE(sock));
+	return simple_xattr_get(&sockfs_xa_cache, &si->xattrs, name, value, size);
+}
+
 static const struct xattr_handler * const sockfs_xattr_handlers[] = {
 	&sockfs_xattr_handler,
 	&sockfs_security_xattr_handler,