Re: [PATCH bpf-next 0/4] Make inode storage available to tracing prog

[Casey Schaufler <casey@schaufler-ca.com>]

On 11/12/2024 10:44 AM, Song Liu wrote:
> Hi Casey, 
>
> Thanks for your input. 
>
>> On Nov 12, 2024, at 10:09 AM, Casey Schaufler <casey@schaufler-ca.com> wrote:
>>
>> On 11/12/2024 12:25 AM, Song Liu wrote:
>>> bpf inode local storage can be useful beyond LSM programs. For example,
>>> bcc/libbpf-tools file* can use inode local storage to simplify the logic.
>>> This set makes inode local storage available to tracing program.
>> Mixing the storage and scope of LSM data and tracing data leaves all sorts
>> of opportunities for abuse. Add inode data for tracing if you can get the
>> patch accepted, but do not move the LSM data out of i_security. Moving
>> the LSM data would break the integrity (such that there is) of the LSM
>> model.
> I honestly don't see how this would cause any issues. Each bpf inode 
> storage maps are independent of each other, and the bpf local storage is 
> designed to handle multiple inode storage maps properly. Therefore, if
> the user decide to stick with only LSM hooks, there isn't any behavior 
> change. OTOH, if the user decides some tracing hooks (on tracepoints, 
> etc.) are needed, making a inode storage map available for both tracing 
> programs and LSM programs would help simplify the logic. (Alternatively,
> the tracing programs need to store per inode data in a hash map, and 
> the LSM program would read that instead of the inode storage map.)
>
> Does this answer the question and address the concerns?

First off, I had no question. No, this does not address my concern.
LSM data should be kept in and managed by the LSMs. We're making an
effort to make the LSM infrastructure more consistent. Moving some of
the LSM data into an LSM specific field in the inode structure goes
against this. What you're proposing is a one-off clever optimization
hack. We have too many of those already.



>
> Thanks,
> Song
>
>>> 1/4 is missing change for bpf task local storage. 2/4 move inode local
>>> storage from security blob to inode.
>>>
>>> Similar to task local storage in tracing program, it is necessary to add
>>> recursion prevention logic for inode local storage. Patch 3/4 adds such
>>> logic, and 4/4 add a test for the recursion prevention logic.
>>>
>>> Song Liu (4):
>>>  bpf: lsm: Remove hook to bpf_task_storage_free
>>>  bpf: Make bpf inode storage available to tracing program
>>>  bpf: Add recursion prevention logic for inode storage
>>>  selftest/bpf: Test inode local storage recursion prevention
> [...]
>