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.
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
fs/pidfs.c | 70 +++++++++++++++++++++++++++++++++++++---------
include/uapi/linux/pidfd.h | 3 +-
2 files changed, 59 insertions(+), 14 deletions(-)
diff --git a/fs/pidfs.c b/fs/pidfs.c
index 433f676c066c..e500bc4c5af2 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -32,11 +32,12 @@ static struct kmem_cache *pidfs_cachep __ro_after_init;
*/
struct pidfs_exit_info {
__u64 cgroupid;
- __u64 exit_code;
+ __s32 exit_code;
};
struct pidfs_inode {
- struct pidfs_exit_info exit_info;
+ struct pidfs_exit_info __pei;
+ struct pidfs_exit_info *exit_info;
struct inode vfs_inode;
};
@@ -228,11 +229,14 @@ 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 long pidfd_info(struct file *file, struct task_struct *task,
+ unsigned int cmd, unsigned long arg)
{
struct pidfd_info __user *uinfo = (struct pidfd_info __user *)arg;
size_t usize = _IOC_SIZE(cmd);
struct pidfd_info kinfo = {};
+ struct pidfs_exit_info *exit_info;
+ struct inode *inode = file_inode(file);
struct user_namespace *user_ns;
const struct cred *c;
__u64 mask;
@@ -248,6 +252,39 @@ static long pidfd_info(struct task_struct *task, unsigned int cmd, unsigned long
if (copy_from_user(&mask, &uinfo->mask, sizeof(mask)))
return -EFAULT;
+ exit_info = READ_ONCE(pidfs_i(inode)->exit_info);
+ if (exit_info) {
+ /*
+ * TODO: Oleg, I didn't see a reason for putting
+ * retrieval of the exit status of a task behind some
+ * form of permission check. Maybe there's some
+ * potential concerns with seeing the exit status of a
+ * SIGKILLed suid binary or something but even then I'm
+ * not sure that's a problem.
+ *
+ * If we want this we could put this behind some *uid
+ * check similar to what ptrace access does by recording
+ * parts of the creds we'd need for checking this. But
+ * only if we really need it.
+ */
+ kinfo.exit_code = exit_info->exit_code;
+#ifdef CONFIG_CGROUPS
+ kinfo.cgroupid = exit_info->cgroupid;
+ kinfo.mask |= PIDFD_INFO_EXIT | PIDFD_INFO_CGROUPID;
+#endif
+ }
+
+ /*
+ * If the task has already been reaped only exit information
+ * can be provided. It's entirely possible that the task has
+ * already been reaped but we managed to grab a reference to it
+ * before that. So a full set of information about @task doesn't
+ * mean it hasn't been waited upon. Similarly, a full set of
+ * information doesn't mean that the task hasn't already exited.
+ */
+ if (!task)
+ goto copy_out;
+
c = get_task_cred(task);
if (!c)
return -ESRCH;
@@ -267,11 +304,13 @@ 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) {
+ rcu_read_lock();
+ cgrp = task_dfl_cgroup(task);
+ kinfo.cgroupid = cgroup_id(cgrp);
+ kinfo.mask |= PIDFD_INFO_CGROUPID;
+ rcu_read_unlock();
+ }
#endif
/*
@@ -291,6 +330,7 @@ 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
@@ -341,12 +381,13 @@ static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
}
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, task, cmd, arg);
+
+ if (!task)
+ return -ESRCH;
if (arg)
return -EINVAL;
@@ -486,7 +527,7 @@ void pidfs_exit(struct task_struct *tsk)
struct cgroup *cgrp;
#endif
inode = d_inode(dentry);
- exit_info = &pidfs_i(inode)->exit_info;
+ exit_info = &pidfs_i(inode)->__pei;
/* TODO: Annoy Oleg to tell me how to do this correctly. */
if (tsk->signal->flags & SIGNAL_GROUP_EXIT)
@@ -501,6 +542,8 @@ void pidfs_exit(struct task_struct *tsk)
rcu_read_unlock();
#endif
+ /* Ensure that PIDFD_GET_INFO sees either all or nothing. */
+ smp_store_release(&pidfs_i(inode)->exit_info, &pidfs_i(inode)->__pei);
dput(dentry);
}
}
@@ -568,7 +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..e5966f1a7743 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) /* Always returned if available, even if not 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
