Re: [PATCH net-next v3 3/4] net: core: add getsockopt SO_PEERPIDFD

[Christian Brauner <brauner@kernel.org>]

On Tue, Apr 11, 2023 at 12:42:30PM +0200, Alexander Mikhalitsyn wrote:
> Add SO_PEERPIDFD which allows to get pidfd of peer socket holder pidfd.
> This thing is direct analog of SO_PEERCRED which allows to get plain PID.
> 
> 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: Leon Romanovsky <leon@kernel.org>
> Cc: David Ahern <dsahern@kernel.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Kees Cook <keescook@chromium.org>
> 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: linux-kernel@vger.kernel.org
> Cc: netdev@vger.kernel.org
> Cc: linux-arch@vger.kernel.org
> Tested-by: Luca Boccassi <bluca@debian.org>
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
> ---
> v3:
> 	- fixed possible fd leak (thanks to Christian Brauner)
> v2:
> 	According to review comments from Kuniyuki Iwashima and Christian Brauner:
> 	- use pidfd_create(..) retval as a result
> 	- whitespace change
> ---
>  arch/alpha/include/uapi/asm/socket.h    |  1 +
>  arch/mips/include/uapi/asm/socket.h     |  1 +
>  arch/parisc/include/uapi/asm/socket.h   |  1 +
>  arch/sparc/include/uapi/asm/socket.h    |  1 +
>  include/uapi/asm-generic/socket.h       |  1 +
>  net/core/sock.c                         | 33 +++++++++++++++++++++++++
>  net/socket.c                            |  7 ++++++
>  tools/include/uapi/asm-generic/socket.h |  1 +
>  8 files changed, 46 insertions(+)
> 
> diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
> index ff310613ae64..e94f621903fe 100644
> --- a/arch/alpha/include/uapi/asm/socket.h
> +++ b/arch/alpha/include/uapi/asm/socket.h
> @@ -138,6 +138,7 @@
>  #define SO_RCVMARK		75
>  
>  #define SO_PASSPIDFD		76
> +#define SO_PEERPIDFD		77
>  
>  #if !defined(__KERNEL__)
>  
> diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
> index 762dcb80e4ec..60ebaed28a4c 100644
> --- a/arch/mips/include/uapi/asm/socket.h
> +++ b/arch/mips/include/uapi/asm/socket.h
> @@ -149,6 +149,7 @@
>  #define SO_RCVMARK		75
>  
>  #define SO_PASSPIDFD		76
> +#define SO_PEERPIDFD		77
>  
>  #if !defined(__KERNEL__)
>  
> diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
> index df16a3e16d64..be264c2b1a11 100644
> --- a/arch/parisc/include/uapi/asm/socket.h
> +++ b/arch/parisc/include/uapi/asm/socket.h
> @@ -130,6 +130,7 @@
>  #define SO_RCVMARK		0x4049
>  
>  #define SO_PASSPIDFD		0x404A
> +#define SO_PEERPIDFD		0x404B
>  
>  #if !defined(__KERNEL__)
>  
> diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
> index 6e2847804fea..682da3714686 100644
> --- a/arch/sparc/include/uapi/asm/socket.h
> +++ b/arch/sparc/include/uapi/asm/socket.h
> @@ -131,6 +131,7 @@
>  #define SO_RCVMARK               0x0054
>  
>  #define SO_PASSPIDFD             0x0055
> +#define SO_PEERPIDFD             0x0056
>  
>  #if !defined(__KERNEL__)
>  
> diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
> index b76169fdb80b..8ce8a39a1e5f 100644
> --- a/include/uapi/asm-generic/socket.h
> +++ b/include/uapi/asm-generic/socket.h
> @@ -133,6 +133,7 @@
>  #define SO_RCVMARK		75
>  
>  #define SO_PASSPIDFD		76
> +#define SO_PEERPIDFD		77
>  
>  #if !defined(__KERNEL__)
>  
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 3f974246ba3e..2b040a69e355 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1763,6 +1763,39 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
>  		goto lenout;
>  	}
>  
> +	case SO_PEERPIDFD:
> +	{
> +		struct pid *peer_pid;
> +		struct file *pidfd_file = NULL;
> +		int pidfd;
> +
> +		if (len > sizeof(pidfd))
> +			len = sizeof(pidfd);
> +
> +		spin_lock(&sk->sk_peer_lock);
> +		peer_pid = get_pid(sk->sk_peer_pid);
> +		spin_unlock(&sk->sk_peer_lock);
> +
> +		pidfd = pidfd_prepare(peer_pid, 0, &pidfd_file);
> +
> +		put_pid(peer_pid);

Would be a bit nicer if this would be:

	pidfd = pidfd_prepare(peer_pid, 0, &pidfd_file);
	put_pid(peer_pid);
	if (pidfd < 0)
		return pidfd;
	if (copy_to_sockptr(optval, &pidfd, len) ||
	    copy_to_sockptr(optlen, &len, sizeof(int)))
		return -EFAULT;
	
	fd_install(pidfd, pidfd_file);
	return 0;

Otherwise seems good enough to me.

> +
> +		if (copy_to_sockptr(optval, &pidfd, len) ||
> +		    copy_to_sockptr(optlen, &len, sizeof(int))) {
> +			if (pidfd >= 0) {
> +				put_unused_fd(pidfd);
> +				fput(pidfd_file);
> +			}
> +
> +			return -EFAULT;
> +		}
> +
> +		if (pidfd_file)
> +			fd_install(pidfd, pidfd_file);
> +
> +		return 0;
> +	}
> +
>  	case SO_PEERGROUPS:
>  	{
>  		const struct cred *cred;
> diff --git a/net/socket.c b/net/socket.c
> index 9c1ef11de23f..505b85489354 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -2248,6 +2248,13 @@ static bool sockopt_installs_fd(int level, int optname)
>  		default:
>  			return false;
>  		}
> +	} else if (level == SOL_SOCKET) {
> +		switch (optname) {
> +		case SO_PEERPIDFD:
> +			return true;
> +		default:
> +			return false;
> +		}
>  	}
>  
>  	return false;
> diff --git a/tools/include/uapi/asm-generic/socket.h b/tools/include/uapi/asm-generic/socket.h
> index fbbc4bf53ee3..54d9c8bf7c55 100644
> --- a/tools/include/uapi/asm-generic/socket.h
> +++ b/tools/include/uapi/asm-generic/socket.h
> @@ -122,6 +122,7 @@
>  #define SO_RCVMARK		75
>  
>  #define SO_PASSPIDFD		76
> +#define SO_PEERPIDFD		77
>  
>  #if !defined(__KERNEL__)
>  
> -- 
> 2.34.1
>