Merge tag 'vfs-7.2-rc1.procfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Merge tag 'vfs-7.2-rc1.procfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull procfs updates from Christian Brauner:

 - Revamp fs/filesystems.c

   The file was a mess with a hand-rolled linked list in desperate need
   of a cleanup. The filesystems list is now RCU-ified, /proc files can
   be marked permanent from outside fs/proc/, and the string emitted
   when reading /proc/filesystems is pre-generated and cached instead of
   pointer-chasing and printfing entry by entry on every read.

   The file is read frequently because libselinux reads it and is linked
   into numerous frequently used programs (even ones you would not
   suspect, like sed!). Scalability also improves since reference
   maintenance on open/close is bypassed.

    open+read+close cycle single-threaded (ops/s):
      before: 442732
      after:  1063462 (+140%)

    open+read+close cycle with 20 processes (ops/s):
      before: 606177
      after:  3300576 (+444%)

   A follow-up patch adds missing unlocks in some corner cases and
   tidies things up.

 - Relax the mount visibility check for subset=pid mounts

   When procfs is mounted with subset=pid, all static files become
   unavailable and only the dynamic pid information is accessible. In
   that case there is no point in imposing the full mount visibility
   restrictions on the mounter - everything that can be hidden in procfs
   is already inaccessible. These restrictions prevented procfs from
   being mounted inside rootless containers since almost all container
   implementations overmount parts of procfs to hide certain
   directories.

   As part of this /proc/self/net is only shown in subset=pid mounts for
   CAP_NET_ADMIN, reconfiguring subset=pid is rejected, the
   SB_I_USERNS_VISIBLE superblock flag is replaced with an
   FS_USERNS_MOUNT_RESTRICTED filesystem flag, fully visible mounts are
   recorded in a list, and the mount restrictions are finally
   documented.

 - Protect ptrace_may_access() with exec_update_lock in procfs

   Most uses of ptrace_may_access() in procfs should hold
   exec_update_lock to avoid TOCTOU issues with concurrent privileged
   execve() (like setuid binary execution).

   This fixes the easy cases - the owner and visibility checks and the
   FD link permission checks - with the gnarlier ones to follow later.

* tag 'vfs-7.2-rc1.procfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  fs: fix ups and tidy ups to /proc/filesystems caching
  proc: protect ptrace_may_access() with exec_update_lock (FD links)
  proc: protect ptrace_may_access() with exec_update_lock (part 1)
  docs: proc: add documentation about mount restrictions
  proc: handle subset=pid separately in userns visibility checks
  proc: prevent reconfiguring subset=pid
  proc: subset=pid: Show /proc/self/net only for CAP_NET_ADMIN
  fs: cache the string generated by reading /proc/filesystems
  sysfs: remove trivial sysfs_get_tree() wrapper
  fs: RCU-ify filesystems list
  fs: move SB_I_USERNS_VISIBLE to FS_USERNS_MOUNT_RESTRICTED
  proc: allow to mark /proc files permanent outside of fs/proc/
  namespace: record fully visible mounts in list