On 14/11/2024 08:02, Amir Goldstein wrote: > 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. pid.ino is exposed, but the init-ns pid isn't exposed anywhere to my knowledge. >> 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. I can revert that if you prefer. I squashed them because there was some churn when adding the init-ns-pid necessary to restore them, but I am happy to do things in two steps. Do you prefer having the final handle format in the first step, or letting it evolve into final form over the series?
