On Thu, Mar 16, 2023 at 02:15:25PM +0100, 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@xxxxxxxxxxxxx>
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> Cc: Leon Romanovsky <leon@xxxxxxxxxx>
> Cc: David Ahern <dsahern@xxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Christian Brauner <brauner@xxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: netdev@xxxxxxxxxxxxxxx
> Cc: linux-arch@xxxxxxxxxxxxxxx
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> ---
> 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 | 24 ++++++++++++++++++++++++
> tools/include/uapi/asm-generic/socket.h | 1 +
> 7 files changed, 30 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..3aa1ccd4bcf3 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1763,6 +1763,30 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
> goto lenout;
> }
>
> + case SO_PEERPIDFD:
> + {
> + struct pid *peer_pid;
> + 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);
> +
> + if (!peer_pid ||
> + !pid_has_task(peer_pid, PIDTYPE_TGID))
> + pidfd = -ESRCH;
Any specific reason you want -ESRCH here?
pidfd_create() returns -EINVAL for exactly this check it performs mainly
because the non-existence of PIDTYPE_TGID could either indicate that
this struct pid isn't used as a thread-group leader or - indeed - that
the process has already been reaped. IOW, if there's no specific reason
I would not deviate from pidfd_create()'s return value.
