binfmt_misc: fix crash when load/unload module

We should unregister the table upon module unload otherwise something
horrible will happen when we load binfmt_misc module again.  Also note
that we should keep value returned by register_sysctl_mount_point() and
release it later, otherwise it will leak.

Also, per Christian's comment, to fully restore the old behavior that
won't break userspace the check(binfmt_misc_header) should be
eliminated.

To reproduce:
  modprobe binfmt_misc
  modprobe -r binfmt_misc
  modprobe binfmt_misc
  modprobe -r binfmt_misc
  modprobe binfmt_misc

resulting in

  modprobe: can't load module binfmt_misc (kernel/fs/binfmt_misc.ko): Cannot allocate memory

and an unhappy kernel:

  binfmt_misc: Failed to create fs/binfmt_misc sysctl mount point
  binfmt_misc: Failed to create fs/binfmt_misc sysctl mount point
  BUG: unable to handle page fault for address: fffffbfff8004802
  Call Trace:
    init_misc_binfmt+0x2d/0x1000 [binfmt_misc]

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 3ba442d5331f ("fs: move binfmt_misc sysctl to its own file")
Signed-off-by: Tong Zhang <[email protected]>
Co-developed-by: Christian Brauner<[email protected]>
Acked-by: Luis Chamberlain <[email protected]>
Cc: Eric Biederman <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Iurii Zaikin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions