Re: [PATCH v4 00/19] LSM: Module stacking for SARA and Landlock

[Tetsuo Handa]

On 2018/09/25 1:15, Casey Schaufler wrote:
>>>> ÂÂ Since all free hooks are called when one of init hooks failed, each
>>>> ÂÂ free hook needs to check whether init hook was called. An example is
>>>> ÂÂ inode_free_security() in security/selinux/hooks.c (but not addressed in
>>>> ÂÂ this patch).
>>>
>>> I *think* that selinux_inode_free_security() is safe in this
>>> case because the blob will be zeroed, hence isec->list will
>>> be NULL.
>>
>> That's not safe - look more closely at what list_empty_careful() tests, and then think about what happens when list_del_init() gets called on that isec->list. selinux_inode_free_security() presumes that selinux_inode_alloc_security() has been called already. If you are breaking that assumption, you have to fix it.
> 
> Yup. I misread the macro my first time around. Easy fix.

Oh, I didn't notice that it is doing !list_empty_careful() than list_empty_careful().
Unsafe indeed. But easy to fix.

> 
>> Is there a reason you can't make inode_alloc_security() return void since you moved the allocation to the framework? 
> 
> No reason with any of the existing modules, But I could see someone
> doing unnatural things during allocation that might result in a
> failure.

Currently upstreamed LSM modules and AKARI would be OK. But I can't guarantee it
for future / not-yet-upstreamed LSM modules.