On Thu, May 16, 2019 at 3:08 PM Christian Brauner christian@brauner.io wrote:
On Wed, May 15, 2019 at 10:45:06AM -0700, Daniel Colascione wrote:
On Wed, May 15, 2019 at 3:04 AM Christian Brauner christian@brauner.io wrote:
This adds the pidfd_open() syscall. It allows a caller to retrieve pollable pidfds for a process which did not get created via CLONE_PIDFD, i.e. for a process that is created via traditional fork()/clone() calls that is only referenced by a PID:
[...]
+/**
- 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).
- 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) +{
[...]
if (pid <= 0)return -EINVAL;WDYT of defining pid == 0 to mean "open myself"?
I'm torn. It be a nice shortcut of course but pid being 0 is usually an indicator for child processes. So unless the getpid() before pidfd_open() is an issue I'd say let's leave it as is. If you really want the shortcut might -1 be better?
Joining the bikeshed painting club: Please don't allow either 0 or -1 as shortcut for "self". James Forshaw found an Android security bug a while back (https://bugs.chromium.org/p/project-zero/issues/detail?id=727) that passed a PID to getpidcon(), except that the PID was 0 (placeholder for oneway binder transactions), and then the service thought it was talking to itself. You could pick some other number and provide a #define for that, but I think pidfd_open(getpid(), ...) makes more sense.