Merge tag 'vfs-7.3-rc1.binfmt' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull binfmt updates from Christian Brauner:
 "This contains a bunch of work for binfmt_misc. It fixes a bunch of
  old bugs, reworks the locking, and then extends the format registry
  so a binary type can be matched programmatically and its interpreter
  computed per exec instead of being a fixed string recorded at
  registration time.

  This allows nixos and other to e.g., implement relocatable binaries
  meaning the interpreter/dynamic loader can be determined
  programatically, say found relative to the binary. The mechanism is
  flexible and can support other policies:

   - Handler lookup is now an rcu walk. An exec that matches no
     binfmt_misc entry should now never write to a shared cacheline

   - remove the VERBOSE_STATUS and USE_DEBUG compile time toggles

   - convert the entry file to a seq_file which simplifies things quite
     a bit and kills a lot of custom logic

   - make flags proper enums

   - rename struct Node to binfmt_misc_entry

   - allow entries to be removed with unlink(2)

   - Add the ability to attach bpf programs to binfmt_misc entries so
     it's possible to dynamically choose the execution environment such
     as the loader or interpreter on a per binary basis.

     A handler is an instance of a binfmt_misc_ops struct_ops with a
     ->match() and a ->load() program. match() decides from the entry
     lookup walk whether the handler applies under the same
     registration-order. It can read file content as needed not only the
     prefetched 256 bytes in bprm->buf.

     load() then selects the interpreter and stages it through the new
     bpf_binprm_set_interp(), bpf_binprm_set_interp_arg() and
     bpf_binprm_set_flags() kfuncs.

     Handlers are published in a registry keyed by the registering
     task's user namespace and activated through the existing text
     interface with a new 'B' type carrying the handler name:

	echo ':origin:B::::nix:' > /proc/sys/fs/binfmt_misc/register

     The permission and namespacing model is unchanged. Activating a
     handler requires the same write access to an instance as any other
     registration. A container mounting its own instance escapes the
     host's entries exactly as before. The computed interpreter is
     opened with open_exec() under the caller's credentials and goes
     through full LSM vetting as the next binprm level. A program can
     only ever redirect the caller to something the caller could exec
     anyway.

   - Two dispatch modes are added. So far the chosen interpreter owns
     the whole process identity (argv[0], /proc/pid/cmdline,
     /proc/self/exe all name interpreter information). So relocatable
     find the dynamic linker instead. Also a binary passed to execveat()
     as an inaccessible O_CLOEXEC fd cannot run at all and gdb trips
     because AT_ENTRY and AT_PHDR do not match the exe file. So PIE
     symbols are unrelocated.

     This adds transparent dispatch which allows the interpreter to load
     the binary through AT_EXECFD and leaves the argument vector exactly
     as the caller built it and labels mm->exe_file and comm with the
     binary. It also raises the AT_FLAGS_TRANSPARENT_INTERP aux vector
     bit. The interpreter keeps control of mapping the binary.

     The second mode is loader substitution. This allows a binary to be
     executed natively and only the interpreter to be changed.

   - Last, interpreters can be bound at registration time. Each
     interpreter is opened by its own write with the credentials the
     entry file was opened with. The program picks one per exec with
     bpf_binprm_select_interp().

     Ucounts are used to properly account for pre-opened interpreters
     via /proc/sys/user/max_binfmt_misc_interpreters"

* tag 'vfs-7.3-rc1.binfmt' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (63 commits)
  binfmt_misc: document the pre-opened interpreter limit
  selftests/exec: test the pre-opened interpreter limit
  binfmt_misc: correctly account pre-opened interpreters
  binfmt_misc: document interpreters bound by a 'B' entry
  selftests/exec: test interpreters bound to a 'B' entry
  binfmt_misc: let a 'B' entry bind its interpreters
  binfmt_misc: carry pre-opened interpreters in struct binfmt_misc_interp
  selftests/exec: share the bpf handler preconditions
  binfmt_misc: document registering an entry disabled
  selftests/exec: test registering an entry disabled
  selftests/exec: let binfmt_flag_supported() return a bool
  selftests/exec: check that a binfmt_misc instance cannot be pinned
  binfmt_misc: let a register string create an entry disabled
  binfmt_misc: document loader substitution
  selftests/exec: test binfmt_misc loader substitution
  binfmt_misc: let a bpf handler request loader substitution
  binfmt_misc: add the 'L' loader substitution flag
  binfmt_elf_fdpic: consume a stashed PT_INTERP substitute
  binfmt_elf: consume a stashed PT_INTERP substitute
  exec: carry a PT_INTERP substitute in struct linux_binprm
  ...

diff --cc fs/binfmt_misc.c
Simple merge