Merge branch 'net-move-getsockopt-away-from-__user-buffers'

Breno Leitao says:

====================
net: move .getsockopt away from __user buffers

Currently, the .getsockopt callback requires __user pointers:

  int (*getsockopt)(struct socket *sock, int level,
                    int optname, char __user *optval, int __user *optlen);

This prevents kernel callers (io_uring, BPF) from using getsockopt on
levels other than SOL_SOCKET, since they pass kernel pointers.

Following Linus' suggestion [0], this series introduces sockopt_t, a
type-safe wrapper around iov_iter, and a getsockopt_iter callback that
works with both user and kernel buffers. AF_PACKET and CAN raw are
converted as initial users, with selftests covering the trickiest
conversion patterns.

[0] https://lore.kernel.org/all/CAHk-=whmzrO-BMU=uSVXbuoLi-3tJsO=0kHj1BCPBE3F2kVhTA@mail.gmail.com/
====================

Link: https://patch.msgid.link/20260408-getsockopt-v3-0-061bb9cb355d@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/include/linux/net.h b/include/linux/net.h
index ca6a7bc5c9ae..f268f395ce47 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -23,9 +23,30 @@
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/sockptr.h>
+#include <linux/uio.h>
 
 #include <uapi/linux/net.h>
 
+/**
+ * struct sockopt - socket option value container
+ * @iter_in: iov_iter for reading optval with the content from the caller.
+ *	     Use copy_from_iter() given this iov direction is ITER_SOURCE
+ * @iter_out: iov_iter for protocols to update optval data to userspace
+ *	      Use _copy_to_iter() given iov direction is ITER_DEST
+ * @optlen: serves as both input (buffer size) and output (returned data size).
+ *
+ * Type-safe wrapper for socket option data that works with both
+ * user and kernel buffers.
+ *
+ * The optlen field allows callbacks to return a specific length value
+ * independent of the bytes written via copy_to_iter().
+ */
+typedef struct sockopt {
+	struct iov_iter iter_in;
+	struct iov_iter iter_out;
+	int optlen;
+} sockopt_t;
+
 struct poll_table_struct;
 struct pipe_inode_info;
 struct inode;
@@ -192,6 +213,8 @@ struct proto_ops {
 				      unsigned int optlen);
 	int		(*getsockopt)(struct socket *sock, int level,
 				      int optname, char __user *optval, int __user *optlen);
+	int		(*getsockopt_iter)(struct socket *sock, int level,
+					   int optname, sockopt_t *opt);
 	void		(*show_fdinfo)(struct seq_file *m, struct socket *sock);
 	int		(*sendmsg)   (struct socket *sock, struct msghdr *m,
 				      size_t total_len);