[PATCH net-next 2/4] net: core: add getsockopt SO_PEERCGROUPID

[Alexander Mikhalitsyn]

Add SO_PEERCGROUPID which allows to get cgroup_id
for a socket.

We already have analogical interfaces to retrieve this
information:
- inet_diag: INET_DIAG_CGROUP_ID
- eBPF: bpf_sk_cgroup_id

Having getsockopt() interface makes sense for many
applications, because using eBPF is not always an option,
while inet_diag has obvious complexety and performance drawbacks
if we only want to get this specific info for one specific socket.

Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Cc: cgroups@xxxxxxxxxxxxxxx
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: Willem de Bruijn <willemb@xxxxxxxxxx>
Cc: Leon Romanovsky <leon@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Cc: Lennart Poettering <mzxreary@xxxxxxxxxxx>
Cc: Luca Boccassi <bluca@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: "Michal Koutný" <mkoutny@xxxxxxxx>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
---
 arch/alpha/include/uapi/asm/socket.h    |  2 +
 arch/mips/include/uapi/asm/socket.h     |  2 +
 arch/parisc/include/uapi/asm/socket.h   |  2 +
 arch/sparc/include/uapi/asm/socket.h    |  2 +
 include/uapi/asm-generic/socket.h       |  2 +
 net/core/sock.c                         | 17 +++++++
 net/unix/af_unix.c                      | 63 +++++++++++++++++++++++++
 tools/include/uapi/asm-generic/socket.h |  2 +
 8 files changed, 92 insertions(+)

diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
index 3df5f2dd4c0f..58ce457b2c09 100644
--- a/arch/alpha/include/uapi/asm/socket.h
+++ b/arch/alpha/include/uapi/asm/socket.h
@@ -150,6 +150,8 @@
 
 #define SO_RCVPRIORITY		82
 
+#define SO_PEERCGROUPID		83
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64
diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
index 22fa8f19924a..823fa67f7d79 100644
--- a/arch/mips/include/uapi/asm/socket.h
+++ b/arch/mips/include/uapi/asm/socket.h
@@ -161,6 +161,8 @@
 
 #define SO_RCVPRIORITY		82
 
+#define SO_PEERCGROUPID		83
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64
diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
index aa9cd4b951fe..1ee2e858d177 100644
--- a/arch/parisc/include/uapi/asm/socket.h
+++ b/arch/parisc/include/uapi/asm/socket.h
@@ -142,6 +142,8 @@
 
 #define SO_RCVPRIORITY		0x404D
 
+#define SO_PEERCGROUPID		0x404E
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64
diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
index 5b464a568664..2fe7d0c48a63 100644
--- a/arch/sparc/include/uapi/asm/socket.h
+++ b/arch/sparc/include/uapi/asm/socket.h
@@ -143,6 +143,8 @@
 
 #define SO_RCVPRIORITY           0x005b
 
+#define SO_PEERCGROUPID          0x005c
+
 #if !defined(__KERNEL__)
 
 
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index aa5016ff3d91..903904bb537c 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -145,6 +145,8 @@
 
 #define SO_RCVPRIORITY		82
 
+#define SO_PEERCGROUPID		83
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
diff --git a/net/core/sock.c b/net/core/sock.c
index a0598518ce89..6dc0b1a8367b 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1946,6 +1946,23 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 		goto lenout;
 	}
 
+#ifdef CONFIG_SOCK_CGROUP_DATA
+	case SO_PEERCGROUPID:
+	{
+		const struct proto_ops *ops;
+
+		if (sk->sk_family != AF_UNIX)
+			return -EOPNOTSUPP;
+
+		ops = READ_ONCE(sock->ops);
+		if (!ops->getsockopt)
+			return -EOPNOTSUPP;
+
+		return ops->getsockopt(sock, SOL_SOCKET, optname, optval.user,
+				       optlen.user);
+	}
+#endif
+
 	/* Dubious BSD thing... Probably nobody even uses it, but
 	 * the UNIX standard wants it for whatever reason... -DaveM
 	 */
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 2b2c0036efc9..3455f38f033d 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -901,6 +901,66 @@ static void unix_show_fdinfo(struct seq_file *m, struct socket *sock)
 #define unix_show_fdinfo NULL
 #endif
 
+static int unix_getsockopt(struct socket *sock, int level, int optname,
+			   char __user *optval, int __user *optlen)
+{
+	struct sock *sk = sock->sk;
+
+	union {
+		int val;
+		u64 val64;
+	} v;
+
+	int lv = sizeof(int);
+	int len;
+
+	if (level != SOL_SOCKET)
+		return -ENOPROTOOPT;
+
+	if (get_user(len, optlen))
+		return -EFAULT;
+
+	if (len < 0)
+		return -EINVAL;
+
+	memset(&v, 0, sizeof(v));
+
+	switch (optname) {
+#ifdef CONFIG_SOCK_CGROUP_DATA
+	case SO_PEERCGROUPID:
+	{
+		struct sock *peer;
+		u64 peer_cgroup_id = 0;
+
+		lv = sizeof(u64);
+		if (len < lv)
+			return -EINVAL;
+
+		peer = unix_peer_get(sk);
+		if (!peer)
+			return -ENODATA;
+
+		peer_cgroup_id = cgroup_id(sock_cgroup_ptr(&peer->sk_cgrp_data));
+		sock_put(peer);
+
+		v.val64 = peer_cgroup_id;
+		break;
+	}
+#endif
+	default:
+		return -ENOPROTOOPT;
+	}
+
+	if (len > lv)
+		len = lv;
+	if (copy_to_user(optval, &v, len))
+		return -EFAULT;
+	if (put_user(len, optlen))
+		return -EFAULT;
+
+	return 0;
+}
+
 static const struct proto_ops unix_stream_ops = {
 	.family =	PF_UNIX,
 	.owner =	THIS_MODULE,
@@ -910,6 +970,7 @@ static const struct proto_ops unix_stream_ops = {
 	.socketpair =	unix_socketpair,
 	.accept =	unix_accept,
 	.getname =	unix_getname,
+	.getsockopt =	unix_getsockopt,
 	.poll =		unix_poll,
 	.ioctl =	unix_ioctl,
 #ifdef CONFIG_COMPAT
@@ -935,6 +996,7 @@ static const struct proto_ops unix_dgram_ops = {
 	.socketpair =	unix_socketpair,
 	.accept =	sock_no_accept,
 	.getname =	unix_getname,
+	.getsockopt =	unix_getsockopt,
 	.poll =		unix_dgram_poll,
 	.ioctl =	unix_ioctl,
 #ifdef CONFIG_COMPAT
@@ -959,6 +1021,7 @@ static const struct proto_ops unix_seqpacket_ops = {
 	.socketpair =	unix_socketpair,
 	.accept =	unix_accept,
 	.getname =	unix_getname,
+	.getsockopt =	unix_getsockopt,
 	.poll =		unix_dgram_poll,
 	.ioctl =	unix_ioctl,
 #ifdef CONFIG_COMPAT
diff --git a/tools/include/uapi/asm-generic/socket.h b/tools/include/uapi/asm-generic/socket.h
index aa5016ff3d91..903904bb537c 100644
--- a/tools/include/uapi/asm-generic/socket.h
+++ b/tools/include/uapi/asm-generic/socket.h
@@ -145,6 +145,8 @@
 
 #define SO_RCVPRIORITY		82
 
+#define SO_PEERCGROUPID		83
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
-- 
2.43.0