On Wed, Nov 13, 2024 at 7:01 PM Erin Shepherd <erin.shepherd@xxxxxx> wrote: > > Since the introduction of pidfs, we have had 64-bit process identifiers > that will not be reused for the entire uptime of the system. This greatly > facilitates process tracking in userspace. > > There are two limitations at present: > > * These identifiers are currently only exposed to processes on 64-bit > systems. On 32-bit systems, inode space is also limited to 32 bits and > therefore is subject to the same reuse issues. > * There is no way to go from one of these unique identifiers to a pid or > pidfd. > > This patch implements fh_export and fh_to_dentry which enables userspace to > convert PIDs to and from PID file handles. A process can convert a pidfd into > a file handle using name_to_handle_at, store it (in memory, on disk, or > elsewhere) and then convert it back into a pidfd suing open_by_handle_at. > > To support us going from a file handle to a pidfd, we have to store a pid > inside the file handle. To ensure file handles are invariant and can move > between pid namespaces, we stash a pid from the initial namespace inside > the file handle. > > (There has been some discussion as to whether or not it is OK to include > the PID in the initial pid namespace, but so far there hasn't been any > conclusive reason given as to why this would be a bad idea) IIUC, this is already exposed as st_ino on a 64bit arch? If that is the case, then there is certainly no new info leak in this patch. > > Signed-off-by: Erin Shepherd <erin.shepherd@xxxxxx> > --- > Changes in v2: > - Permit filesystems to opt out of CAP_DAC_READ_SEARCH > - Inline find_pid_ns/get_pid logic; remove unnecessary put_pid > - Squash fh_export & fh_to_dentry into one commit Not sure why you did that. It was pretty nice as separate commits if you ask me. Whatever. Thanks, Amir.
