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pidfs: allow to retrieve exit information

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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: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2025-03-05 11:08:16 +01:00
parent 4513522984
commit 7477d7dce4
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
2 changed files with 70 additions and 19 deletions
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86
fs/pidfs.c
View File

@ -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;
}

3
include/uapi/linux/pidfd.h
View File

@ -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