[PATCH net-next 1/3] netlink: convert to getsockopt_iter

Breno Leitao
2026-05-01T15:53:15Z

Convert AF_NETLINK's getsockopt implementation to use the new
getsockopt_iter callback with sockopt_t.

Key changes:
- Replace (char __user *optval, int __user *optlen) with sockopt_t *opt
- Use opt->optlen for buffer length (input) and returned size (output)
- Use copy_to_iter() instead of put_user()/copy_to_user()
- For NETLINK_LIST_MEMBERSHIPS: walk the groups bitmap and emit each
u32 sequentially via copy_to_iter(), then set opt->optlen to the
total size required (ALIGN(BITS_TO_BYTES(ngroups), sizeof(u32))).
The wrapper writes opt->optlen back to userspace even on partial
failure, preserving the existing API that lets userspace discover
the needed allocation size.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
net/netlink/af_netlink.c | 21 +++++++++++----------
1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 2aeb0680807d6..db3be485b4804 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -39,6 +39,7 @@
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
+#include <linux/uio.h>
#include <linux/skbuff.h>
#include <linux/netdevice.h>
#include <linux/rtnetlink.h>
@@ -1716,18 +1717,18 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
}

static int netlink_getsockopt(struct socket *sock, int level, int optname,
- char __user *optval, int __user *optlen)
+ sockopt_t *opt)
{
struct sock *sk = sock->sk;
struct netlink_sock *nlk = nlk_sk(sk);
unsigned int flag;
int len, val;
+ u32 group;

if (level != SOL_NETLINK)
return -ENOPROTOOPT;

- if (get_user(len, optlen))
- return -EFAULT;
+ len = opt->optlen;
if (len < 0)
return -EINVAL;

@@ -1751,14 +1752,14 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,

idx = pos / sizeof(unsigned long);
shift = (pos % sizeof(unsigned long)) * 8;
- if (put_user((u32)(nlk->groups[idx] >> shift),
- (u32 __user *)(optval + pos))) {
+ group = (u32)(nlk->groups[idx] >> shift);
+ if (copy_to_iter(&group, sizeof(u32),
+ &opt->iter_out) != sizeof(u32)) {
err = -EFAULT;
break;
}
}
- if (put_user(ALIGN(BITS_TO_BYTES(nlk->ngroups), sizeof(u32)), optlen))
- err = -EFAULT;
+ opt->optlen = ALIGN(BITS_TO_BYTES(nlk->ngroups), sizeof(u32));
netlink_unlock_table();
return err;
}
@@ -1784,8 +1785,8 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
len = sizeof(int);
val = test_bit(flag, &nlk->flags);

- if (put_user(len, optlen) ||
- copy_to_user(optval, &val, len))
+ opt->optlen = len;
+ if (copy_to_iter(&val, len, &opt->iter_out) != len)
return -EFAULT;

return 0;
@@ -2813,7 +2814,7 @@ static const struct proto_ops netlink_ops = {
.listen = sock_no_listen,
.shutdown = sock_no_shutdown,
.setsockopt = netlink_setsockopt,
- .getsockopt = netlink_getsockopt,
+ .getsockopt_iter = netlink_getsockopt,
.sendmsg = netlink_sendmsg,
.recvmsg = netlink_recvmsg,
.mmap = sock_no_mmap,

--
2.52.0