在 2025年3月5日 星期三 11:08，Christian Brauner <brauner@xxxxxxxxxx> 寫道： > > > Some tools like systemd's jounral need to retrieve the exit and cgroup > information after a process has already been reaped. This can e.g., > happen when retrieving a pidfd via SCM_PIDFD or SCM_PEERPIDFD. > > Link: https://lore.kernel.org/r/20250304-work-pidfs-kill_on_last_close-v2-6-44fdacfaa7b7@xxxxxxxxxx > Reviewed-by: Jeff Layton jlayton@xxxxxxxxxx > > Signed-off-by: Christian Brauner brauner@xxxxxxxxxx > > --- > fs/pidfs.c | 86 ++++++++++++++++++++++++++++++++++++---------- > include/uapi/linux/pidfd.h | 3 +- > 2 files changed, 70 insertions(+), 19 deletions(-) > > diff --git a/fs/pidfs.c b/fs/pidfs.c > index c4e6527013e7..3c630e9d4a62 100644 > --- a/fs/pidfs.c > +++ b/fs/pidfs.c > @@ -36,7 +36,8 @@ struct pidfs_exit_info { > }; > > struct pidfs_inode { > - struct pidfs_exit_info exit_info; > + struct pidfs_exit_info __pei; > + struct pidfs_exit_info *exit_info; > struct inode vfs_inode; > }; > > @@ -228,17 +229,28 @@ static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts) > return poll_flags; > } > > -static long pidfd_info(struct task_struct *task, unsigned int cmd, unsigned long arg) > +static inline bool pid_in_current_pidns(const struct pid *pid) > +{ > + const struct pid_namespace *ns = task_active_pid_ns(current); > + > + if (ns->level <= pid->level) > > + return pid->numbers[ns->level].ns == ns; > > + > + return false; > +} > + > +static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg) > { > struct pidfd_info __user *uinfo = (struct pidfd_info __user *)arg; > + struct inode *inode = file_inode(file); > + struct pid *pid = pidfd_pid(file); > size_t usize = _IOC_SIZE(cmd); > struct pidfd_info kinfo = {}; > + struct pidfs_exit_info *exit_info; > struct user_namespace *user_ns; > + struct task_struct *task; > const struct cred *c; > __u64 mask; > -#ifdef CONFIG_CGROUPS > - struct cgroup *cgrp; > -#endif > > if (!uinfo) > return -EINVAL; > @@ -248,6 +260,37 @@ static long pidfd_info(struct task_struct *task, unsigned int cmd, unsigned long > if (copy_from_user(&mask, &uinfo->mask, sizeof(mask))) > > return -EFAULT; > > + /* > + * Restrict information retrieval to tasks within the caller's pid > + * namespace hierarchy. > + */ > + if (!pid_in_current_pidns(pid)) > + return -ESRCH; > + > + if (mask & PIDFD_INFO_EXIT) { > + exit_info = READ_ONCE(pidfs_i(inode)->exit_info); > > + if (exit_info) { > + kinfo.mask |= PIDFD_INFO_EXIT; > +#ifdef CONFIG_CGROUPS > + kinfo.cgroupid = exit_info->cgroupid; > > + kinfo.mask |= PIDFD_INFO_CGROUPID; > +#endif > + kinfo.exit_code = exit_info->exit_code; > > + } > + } > + > + task = get_pid_task(pid, PIDTYPE_PID); > + if (!task) { > + /* > + * If the task has already been reaped, only exit > + * information is available > + */ > + if (!(mask & PIDFD_INFO_EXIT)) > + return -ESRCH; > + > + goto copy_out; > + } > + > c = get_task_cred(task); > if (!c) > return -ESRCH; > @@ -267,11 +310,15 @@ static long pidfd_info(struct task_struct *task, unsigned int cmd, unsigned long > put_cred(c); > > #ifdef CONFIG_CGROUPS > - rcu_read_lock(); > - cgrp = task_dfl_cgroup(task); > - kinfo.cgroupid = cgroup_id(cgrp); > - kinfo.mask |= PIDFD_INFO_CGROUPID; > - rcu_read_unlock(); > + if (!kinfo.cgroupid) { > + struct cgroup cgrp; > + > + rcu_read_lock(); > + cgrp = task_dfl_cgroup(task); > + kinfo.cgroupid = cgroup_id(cgrp); > + kinfo.mask |= PIDFD_INFO_CGROUPID; > + rcu_read_unlock(); > + } > #endif > > / > @@ -291,6 +338,7 @@ static long pidfd_info(struct task_struct task, unsigned int cmd, unsigned long > if (kinfo.pid == 0 || kinfo.tgid == 0 || (kinfo.ppid == 0 && kinfo.pid != 1)) > return -ESRCH; > > +copy_out: > / > * If userspace and the kernel have the same struct size it can just > * be copied. If userspace provides an older struct, only the bits that > @@ -325,7 +373,6 @@ static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg) > { > struct task_struct *task __free(put_task) = NULL; > struct nsproxy *nsp __free(put_nsproxy) = NULL; > - struct pid *pid = pidfd_pid(file); > struct ns_common *ns_common = NULL; > struct pid_namespace *pid_ns; > > @@ -340,13 +387,13 @@ static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg) > return put_user(file_inode(file)->i_generation, argp); > > } > > - task = get_pid_task(pid, PIDTYPE_PID); > - if (!task) > - return -ESRCH; > - > /* Extensible IOCTL that does not open namespace FDs, take a shortcut */ > if (_IOC_NR(cmd) == _IOC_NR(PIDFD_GET_INFO)) > - return pidfd_info(task, cmd, arg); > + return pidfd_info(file, cmd, arg); > + > + task = get_pid_task(pidfd_pid(file), PIDTYPE_PID); > + if (!task) > + return -ESRCH; > > if (arg) > return -EINVAL; > @@ -484,7 +531,7 @@ void pidfs_exit(struct task_struct *tsk) > dentry = stashed_dentry_get(&task_pid(tsk)->stashed); > > if (dentry) { > struct inode *inode = d_inode(dentry); > - struct pidfs_exit_info *exit_info = &pidfs_i(inode)->exit_info; > > + struct pidfs_exit_info *exit_info = &pidfs_i(inode)->__pei; > > #ifdef CONFIG_CGROUPS > struct cgroup *cgrp; > > @@ -495,6 +542,8 @@ void pidfs_exit(struct task_struct *tsk) > #endif > exit_info->exit_code = tsk->exit_code; > > > + /* Ensure that PIDFD_GET_INFO sees either all or nothing. */ > + smp_store_release(&pidfs_i(inode)->exit_info, &pidfs_i(inode)->__pei); > > dput(dentry); > } > } > @@ -562,7 +611,8 @@ static struct inode *pidfs_alloc_inode(struct super_block *sb) > if (!pi) > return NULL; > > - memset(&pi->exit_info, 0, sizeof(pi->exit_info)); > > + memset(&pi->__pei, 0, sizeof(pi->__pei)); > > + pi->exit_info = NULL; > > > return &pi->vfs_inode; > > } > diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h > index e0abd0b18841..5cd5dcbfe884 100644 > --- a/include/uapi/linux/pidfd.h > +++ b/include/uapi/linux/pidfd.h > @@ -20,6 +20,7 @@ > #define PIDFD_INFO_PID (1UL << 0) /* Always returned, even if not requested / > #define PIDFD_INFO_CREDS (1UL << 1) / Always returned, even if not requested / > #define PIDFD_INFO_CGROUPID (1UL << 2) / Always returned if available, even if not requested / > +#define PIDFD_INFO_EXIT (1UL << 3) / Only returned if requested. / > > #define PIDFD_INFO_SIZE_VER0 64 / sizeof first published struct */ > > @@ -86,7 +87,7 @@ struct pidfd_info { > __u32 sgid; > __u32 fsuid; > __u32 fsgid; > - __u32 spare0[1]; > + __s32 exit_code; > }; > > #define PIDFS_IOCTL_MAGIC 0xFF > > -- > 2.47.2 Acked-by: Mike Yuan <me@xxxxxxxxxxx>
