Re: [PATCH 07/10] net: add SO_PEERPIDFD_THREAD to get a thread-specific pidfd

[Alexander Mikhalitsyn]

Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner
<brauner@xxxxxxxxxx>:
>
> SO_PEERPIDFD hands out a pidfd for the thread-group that called
> connect() or socketpair(). Enable workloads such as the coredump server
> or a broker to get a pidfd of the specific thread that connected to the
> socket.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>

LGTM

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxxx>

> ---
>  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                       | 87 ++++++++++++++++++++---------------
>  net/unix/af_unix.c                    |  1 +
>  7 files changed, 61 insertions(+), 37 deletions(-)
>
> diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
> index bb3d534826bb..5d3524c26b2b 100644
> --- a/arch/alpha/include/uapi/asm/socket.h
> +++ b/arch/alpha/include/uapi/asm/socket.h
> @@ -159,6 +159,8 @@
>
>  #define SO_PASSPIDFD_THREAD    86
>
> +#define SO_PEERPIDFD_THREAD    87
> +
>  #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 269badcaa086..245a43f52fb1 100644
> --- a/arch/mips/include/uapi/asm/socket.h
> +++ b/arch/mips/include/uapi/asm/socket.h
> @@ -170,6 +170,8 @@
>
>  #define SO_PASSPIDFD_THREAD    86
>
> +#define SO_PEERPIDFD_THREAD    87
> +
>  #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 313aee10a52c..f23710e1c671 100644
> --- a/arch/parisc/include/uapi/asm/socket.h
> +++ b/arch/parisc/include/uapi/asm/socket.h
> @@ -151,6 +151,8 @@
>
>  #define SO_PASSPIDFD_THREAD    0x4054
>
> +#define SO_PEERPIDFD_THREAD    0x4055
> +
>  #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 bd3e69bcce7a..b35b25bdefc2 100644
> --- a/arch/sparc/include/uapi/asm/socket.h
> +++ b/arch/sparc/include/uapi/asm/socket.h
> @@ -152,6 +152,8 @@
>
>  #define SO_PASSPIDFD_THREAD      0x005f
>
> +#define SO_PEERPIDFD_THREAD      0x0060
> +
>  #if !defined(__KERNEL__)
>
>
> diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
> index d1e5c6de146d..56fed7ab27ab 100644
> --- a/include/uapi/asm-generic/socket.h
> +++ b/include/uapi/asm-generic/socket.h
> @@ -154,6 +154,8 @@
>
>  #define SO_PASSPIDFD_THREAD    86
>
> +#define SO_PEERPIDFD_THREAD    87
> +
>  #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 6ada7e7eb7d7..cb2ffd329bc6 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1743,6 +1743,50 @@ static int groups_to_user(sockptr_t dst, const struct group_info *src)
>         return 0;
>  }
>
> +/* Hand out a pidfd for @type of the socket's peer via SO_PEERPIDFD*. */
> +static int sk_getsockopt_peerpidfd(struct sock *sk, enum pid_type type,
> +                                  sockptr_t optval, sockptr_t optlen, int len)
> +{
> +       struct file *pidfd_file = NULL;
> +       unsigned int flags = 0;
> +       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[type]);
> +       spin_unlock(&sk->sk_peer_lock);
> +
> +       if (!peer_pid)
> +               return -ENODATA;
> +
> +       /* The use of PIDFD_STALE requires stashing of struct pid on pidfs
> +        * with pidfs_register_pid() and only AF_UNIX were prepared for this.
> +        */
> +       if (sk->sk_family == AF_UNIX)
> +               flags |= PIDFD_STALE;
> +       if (type == PIDTYPE_PID)
> +               flags |= PIDFD_THREAD;
> +
> +       pidfd = pidfd_prepare(peer_pid, flags, &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))) {
> +               put_unused_fd(pidfd);
> +               fput(pidfd_file);
> +
> +               return -EFAULT;
> +       }
> +
> +       fd_install(pidfd, pidfd_file);
> +       return 0;
> +}
> +
>  int sk_getsockopt(struct sock *sk, int level, int optname,
>                   sockptr_t optval, sockptr_t optlen)
>  {
> @@ -1938,45 +1982,14 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
>         }
>
>         case SO_PEERPIDFD:
> -       {
> -               struct pid *peer_pid;
> -               struct file *pidfd_file = NULL;
> -               unsigned int flags = 0;
> -               int pidfd;
> -
> -               if (len > sizeof(pidfd))
> -                       len = sizeof(pidfd);
> -
> -               spin_lock(&sk->sk_peer_lock);
> -               peer_pid = get_pid(sk->sk_peer_pid[PIDTYPE_TGID]);
> -               spin_unlock(&sk->sk_peer_lock);
> -
> -               if (!peer_pid)
> -                       return -ENODATA;
> -
> -               /* The use of PIDFD_STALE requires stashing of struct pid
> -                * on pidfs with pidfs_register_pid() and only AF_UNIX
> -                * were prepared for this.
> -                */
> -               if (sk->sk_family == AF_UNIX)
> -                       flags = PIDFD_STALE;
> +               return sk_getsockopt_peerpidfd(sk, PIDTYPE_TGID, optval, optlen, len);
>
> -               pidfd = pidfd_prepare(peer_pid, flags, &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))) {
> -                       put_unused_fd(pidfd);
> -                       fput(pidfd_file);
> -
> -                       return -EFAULT;
> -               }
> +       case SO_PEERPIDFD_THREAD:
> +               /* Only AF_UNIX records the peer's connecting thread. */
> +               if (!sk_is_unix(sk))
> +                       return -EOPNOTSUPP;
>
> -               fd_install(pidfd, pidfd_file);
> -               return 0;
> -       }
> +               return sk_getsockopt_peerpidfd(sk, PIDTYPE_PID, optval, optlen, len);
>
>         case SO_PEERGROUPS:
>         {
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index d01ee76c8026..563d9827c5cc 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1056,6 +1056,7 @@ static bool unix_bpf_bypass_getsockopt(int level, int optname)
>         if (level == SOL_SOCKET) {
>                 switch (optname) {
>                 case SO_PEERPIDFD:
> +               case SO_PEERPIDFD_THREAD:
>                         return true;
>                 default:
>                         return false;
>
> --
> 2.53.0
>