On Tue, Mar 26, 2019 at 9:34 AM Christian Brauner [off-list ref] wrote:

On Tue, Mar 26, 2019 at 05:31:42PM +0100, Christian Brauner wrote:

quoted

On Tue, Mar 26, 2019 at 05:23:37PM +0100, Christian Brauner wrote:

quoted

On Tue, Mar 26, 2019 at 09:17:07AM -0700, Daniel Colascione wrote:

quoted

Thanks for the patch.

On Tue, Mar 26, 2019 at 8:55 AM Christian Brauner [off-list ref] wrote:

quoted

The pidctl() syscalls builds on, extends, and improves translate_pid() [4].
I quote Konstantins original patchset first that has already been acked and
picked up by Eric before and whose functionality is preserved in this
syscall:

We still haven't had a much-needed conversation about splitting this
system call into smaller logical operations. It's important that we
address this point before this patch is merged and becomes permanent
kernel ABI.

I don't particularly mind splitting this into an additional syscall like
e.g.  pidfd_open() but then we have - and yes, I know you'll say
syscalls are cheap - translate_pid(), and pidfd_open(). What I like
about this rn is that it connects both apis in a single syscall
and allows pidfd retrieval across pid namespaces. So I guess we'll see
what other people think.

There's something to be said for

pidfd_open(pid_t pid, int pidfd, unsigned int flags);

/* get pidfd */
int pidfd = pidfd_open(1234, -1, 0);

/* convert to procfd */
int procfd = pidfd_open(-1, 4, 0);

/* convert to pidfd */
int pidfd = pidfd_open(4, -1, 0);

probably rather:

int pidfd = pidfd_open(-1, 4, PIDFD_TO_PROCFD);

Do you mean:

int procrootfd = open("/proc", O_DIRECTORY | O_RDONLY);
int procfd = pidfd_open(procrootfd, pidfd, PIDFD_TO_PROCFD);

or do you have some other solution in mind to avoid the security problem?