Re: [PATCH 02/10] af_unix: record the pid of the sending thread
From: Alexander Mikhalitsyn <hidden>
Date: 2026-09-07 09:55:36
Also in:
linux-fsdevel, lkml
Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner [off-list ref]:
quoted hunk ↗ jump to hunk
Currently only the struct pid of the thread-group leader is recorded. The identity of the actual thread that sent the message or is connected to a given socket cannot be retrieved. Add the plumbing to make it possible to retrieve a pidfd for the sender. Nothing uses the thread-specific struct pid yet. No functional changes. Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org> --- include/net/scm.h | 7 +++---- net/core/scm.c | 21 +++++++++++++++++---- net/unix/af_unix.c | 23 +++++++++++++---------- net/unix/af_unix.h | 3 ++- 4 files changed, 35 insertions(+), 19 deletions(-)diff --git a/include/net/scm.h b/include/net/scm.h index 86ae6bc109ec..aa7d15c5fc27 100644 --- a/include/net/scm.h +++ b/include/net/scm.h@@ -42,7 +42,7 @@ struct scm_fp_list { }; struct scm_cookie { - struct pid *pid; /* Skb credentials */ + DECLARE_PIDS(pid, PIDTYPE_TGID); /* Skb credentials by pid type */ struct scm_fp_list *fp; /* Passed files */ struct scm_creds creds; /* Skb credentials */ #ifdef CONFIG_SECURITY_NETWORK@@ -69,7 +69,7 @@ static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_co static __inline__ void scm_set_cred(struct scm_cookie *scm, struct pid *pid, kuid_t uid, kgid_t gid) { - scm->pid = get_pid(pid); + scm->pid[PIDTYPE_TGID] = get_pid(pid); scm->creds.pid = pid_vnr(pid); scm->creds.uid = uid; scm->creds.gid = gid;@@ -77,8 +77,7 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm, static __inline__ void scm_destroy_cred(struct scm_cookie *scm) { - put_pid(scm->pid); - scm->pid = NULL; + put_pids(scm->pid); } static __inline__ void scm_destroy(struct scm_cookie *scm)diff --git a/net/core/scm.c b/net/core/scm.c index f0d44ecdb11f..9b9e119c353a 100644 --- a/net/core/scm.c +++ b/net/core/scm.c@@ -149,6 +149,7 @@ EXPORT_SYMBOL(__scm_destroy); static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid) { + struct pid *thread_pid; int err; /* drop all previous references */@@ -158,7 +159,18 @@ static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid) if (unlikely(err)) return err; - scm->pid = pid; + /* A sender naming its own thread-group sends from the current thread. */ + if (pid == task_tgid(current)) + thread_pid = task_pid(current); + else + thread_pid = pid;
Hi Christian,
The patch looks good to me, but this spot raised some doubts for me.
If scm_replace_pid() is called with pid == task_tgid(current) then all
good, because we
get scm->pid[PIDTYPE_TGID] == pid and scm->pid[PIDTYPE_PID] ==
task_pid(current). All good.
If scm_replace_pid() is supplied with pid that has a type PIDTYPE_TGID, then:
- scm->pid[PIDTYPE_TGID] == pid. Good.
- scm->pid[PIDTYPE_PID] = pid. Doesn't looks correct, shoudn't we do
something like:
{
struct task_struct *task;
rcu_read_lock();
task = pid_task(pid, PIDTYPE_TGID);
thread_pid = task_pid(task);
rcu_read_unlock();
}
to get a correct thread_pid for both cases here?
Kind regards,
Alex
quoted hunk ↗ jump to hunk
+ + err = pidfs_register_pid(thread_pid); + if (unlikely(err)) + return err; + + scm->pid[PIDTYPE_TGID] = pid; + scm->pid[PIDTYPE_PID] = get_pid(thread_pid); scm->creds.pid = pid_vnr(pid); return 0; }@@ -207,7 +219,8 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p) if (err) goto error; - if (!p->pid || pid_vnr(p->pid) != creds.pid) { + if (!p->pid[PIDTYPE_TGID] || + pid_vnr(p->pid[PIDTYPE_TGID]) != creds.pid) { struct pid *pid; err = -ESRCH; pid = find_get_pid(creds.pid);@@ -504,10 +517,10 @@ static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm) return; } - if (!scm->pid) + if (!scm->pid[PIDTYPE_TGID]) return; - pidfd = pidfd_prepare(scm->pid, PIDFD_STALE, &pidfd_file); + pidfd = pidfd_prepare(scm->pid[PIDTYPE_TGID], PIDFD_STALE, &pidfd_file); if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) { if (pidfd_file) {diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index 13f9926bf205..011af84e3626 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c@@ -1973,7 +1973,7 @@ static void unix_destruct_scm(struct sk_buff *skb) { struct scm_cookie scm = {}; - swap(scm.pid, UNIXCB(skb).pid); + swap_pids(scm.pid, UNIXCB(skb).pid); if (UNIXCB(skb).fp) unix_detach_fds(&scm, skb);@@ -1991,7 +1991,7 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen { int err = 0; - UNIXCB(skb).pid = get_pid(scm->pid); + get_pids(UNIXCB(skb).pid, scm->pid); UNIXCB(skb).uid = scm->creds.uid; UNIXCB(skb).gid = scm->creds.gid; UNIXCB(skb).fp = NULL;@@ -2005,7 +2005,10 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen static void unix_skb_to_scm(struct sk_buff *skb, struct scm_cookie *scm) { - scm_set_cred(scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid); + get_pids(scm->pid, UNIXCB(skb).pid); + scm->creds.pid = pid_vnr(scm->pid[PIDTYPE_TGID]); + scm->creds.uid = UNIXCB(skb).uid; + scm->creds.gid = UNIXCB(skb).gid; unix_set_secdata(scm, skb); }@@ -2025,20 +2028,20 @@ static void unix_skb_to_scm(struct sk_buff *skb, struct scm_cookie *scm) static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk, const struct sock *other) { - if (UNIXCB(skb).pid) + if (UNIXCB(skb).pid[PIDTYPE_TGID]) return 0; if (unix_may_passcred(sk) || unix_may_passcred(other) || !other->sk_socket) { - struct pid *pid; int err; - pid = task_tgid(current); - err = pidfs_register_pid(pid); - if (unlikely(err)) + get_task_pids(UNIXCB(skb).pid, current); + err = pidfs_register_pids(UNIXCB(skb).pid); + if (unlikely(err)) { + put_pids(UNIXCB(skb).pid); return err; + } - UNIXCB(skb).pid = get_pid(pid); current_uid_gid(&UNIXCB(skb).uid, &UNIXCB(skb).gid); }@@ -2048,7 +2051,7 @@ static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk, static bool unix_skb_scm_eq(struct sk_buff *skb, struct scm_cookie *scm) { - return UNIXCB(skb).pid == scm->pid && + return UNIXCB(skb).pid[PIDTYPE_TGID] == scm->pid[PIDTYPE_TGID] && uid_eq(UNIXCB(skb).uid, scm->creds.uid) && gid_eq(UNIXCB(skb).gid, scm->creds.gid) && unix_secdata_eq(scm, skb);diff --git a/net/unix/af_unix.h b/net/unix/af_unix.h index 8119dbeef3a3..402742895acc 100644 --- a/net/unix/af_unix.h +++ b/net/unix/af_unix.h@@ -2,6 +2,7 @@ #ifndef __AF_UNIX_H #define __AF_UNIX_H +#include <linux/pid_types.h> #include <linux/uidgid.h> #define UNIX_HASH_MOD (256 - 1)@@ -11,7 +12,7 @@ struct sock *unix_peer_get(struct sock *sk); struct unix_skb_parms { - struct pid *pid; /* skb credentials */ + DECLARE_PIDS(pid, PIDTYPE_TGID); /* skb credentials by pid type */ kuid_t uid; kgid_t gid; struct scm_fp_list *fp; /* Passed files */ --2.53.0