[PATCH 07/10] net: add SO_PEERPIDFD_THREAD to get a thread-specific pidfd
From: Christian Brauner
Date: Mon Aug 31 2026 - 07:27:10 EST
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>
---
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