Re: [PATCH 07/10] net: add SO_PEERPIDFD_THREAD to get a thread-specific pidfd
From: Alexander Mikhalitsyn <hidden>
Date: 2026-09-07 10:50:02
Also in:
linux-fsdevel, lkml
Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner [off-list ref]:
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@kernel.org>
LGTM Reviewed-by: Alexander Mikhalitsyn <redacted>
quoted hunk ↗ jump to hunk
--- 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 == 64diff --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 == 64diff --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 == 64diff --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