Re: [PATCH 1/2] pid: add pidfd_open()
From: Yann Droneaud <hidden>
Date: 2019-05-15 14:29:18
Also in:
linux-alpha, linux-api, linux-arch, linux-arm-kernel, linux-kselftest, linux-mips, linux-s390, linux-sh, lkml, sparclinux
Hi, Le mercredi 15 mai 2019 à 12:03 +0200, Christian Brauner a écrit :
quoted hunk ↗ jump to hunk
diff --git a/kernel/pid.c b/kernel/pid.c index 20881598bdfa..237d18d6ecb8 100644 --- a/kernel/pid.c +++ b/kernel/pid.c@@ -451,6 +452,53 @@ struct pid *find_ge_pid(int nr, structpid_namespace *ns) return idr_get_next(&ns->idr, &nr); } +/** + * pidfd_open() - Open new pid file descriptor. + * + * @pid: pid for which to retrieve a pidfd + * @flags: flags to pass + * + * This creates a new pid file descriptor with the O_CLOEXEC flag set for + * the process identified by @pid. Currently, the process identified by + * @pid must be a thread-group leader. This restriction currently exists + * for all aspects of pidfds including pidfd creation (CLONE_PIDFD cannot + * be used with CLONE_THREAD) and pidfd polling (only supports thread group + * leaders). + *
Would it be possible to create file descriptor with "restricted" operation ? - O_RDONLY: waiting for process completion allowed (for example) - O_WRONLY: sending process signal allowed For example, a process could send over a Unix socket a process a pidfd, allowing this to only wait for completion, but not sending signal ? I see the permission check is not done in pidfd_open(), so what prevent a user from sending a signal to another user owned process ? If it's in pidfd_send_signal(), then, passing the socket through SCM_RIGHT won't be useful if the target process is not owned by the same user, or root.
+ * Return: On success, a cloexec pidfd is returned.
+ * On error, a negative errno number will be returned.
+ */
+SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
+{
+ int fd, ret;
+ struct pid *p;
+ struct task_struct *tsk;
+
+ if (flags)
+ return -EINVAL;
+
+ if (pid <= 0)
+ return -EINVAL;
+
+ p = find_get_pid(pid);
+ if (!p)
+ return -ESRCH;
+
+ rcu_read_lock();
+ tsk = pid_task(p, PIDTYPE_PID);
+ if (!tsk)
+ ret = -ESRCH;
+ else if (unlikely(!thread_group_leader(tsk)))
+ ret = -EINVAL;
+ else
+ ret = 0;
+ rcu_read_unlock();
+
+ fd = ret ?: pidfd_create(p);
+ put_pid(p);
+ return fd;
+}
+
void __init pid_idr_init(void)
{
/* Verify no one has done anything silly: */Regards. -- Yann Droneaud OPTEYA