Unverified Commit 7477d7dc authored by Christian Brauner's avatar Christian Brauner
Browse files

pidfs: allow to retrieve exit information 

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/20250305-work-pidfs-kill_on_last_close-v3-6-c8c3d8361705@kernel.org


Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 45135229

fs/pidfs.c

+68 −18
Original line number Diff line number Diff line
@@ -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

	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;

}

include/uapi/linux/pidfd.h

+2 −1
Original line number Diff line number Diff line
@@ -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