Re: [PATCH v2 1/2] binfmt_misc: fix crash when load/unload module

[Luis Chamberlain <mcgrof@kernel.org>]

On Mon, Jan 24, 2022 at 10:18:12AM -0800, Tong Zhang wrote:
> 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.
> 
> reproduce:
> modprobe binfmt_misc
> modprobe -r binfmt_misc
> modprobe binfmt_misc
> modprobe -r binfmt_misc
> modprobe binfmt_misc
> 
> [   18.032038] Call Trace:
> [   18.032108]  <TASK>
> [   18.032169]  dump_stack_lvl+0x34/0x44
> [   18.032273]  __register_sysctl_table+0x6f4/0x720
> [   18.032397]  ? preempt_count_sub+0xf/0xb0
> [   18.032508]  ? 0xffffffffc0040000
> [   18.032600]  init_misc_binfmt+0x2d/0x1000 [binfmt_misc]
> [   18.042520] binfmt_misc: Failed to create fs/binfmt_misc sysctl mount point
> modprobe: can't load module binfmt_misc (kernel/fs/binfmt_misc.ko): Cannot allocate memory
> [   18.063549] binfmt_misc: Failed to create fs/binfmt_misc sysctl mount point
> [   18.204779] BUG: unable to handle page fault for address: fffffbfff8004802
> 
> Fixes: 3ba442d5331f ("fs: move binfmt_misc sysctl to its own file")
> Co-developed-by: Christian Brauner<brauner@kernel.org>
> Signed-off-by: Tong Zhang <ztong0001@gmail.com>

Acked-by: Luis Chamberlain <mcgrof@kernel.org>

  Luis