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

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Alexander Mikhalitsyn wrote:
> 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@vger.kernel.org
> Cc: netdev@vger.kernel.org
> Cc: cgroups@vger.kernel.org
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: Willem de Bruijn <willemb@google.com>
> Cc: Leon Romanovsky <leon@kernel.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
> Cc: Lennart Poettering <mzxreary@0pointer.de>
> Cc: Luca Boccassi <bluca@debian.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: "Michal Koutný" <mkoutny@suse.com>
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
> ---
>  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;

why the union if the only valid use is a u64? Is this forward looking?