Re: [PATCH v2 1/2] procfs: avoid some usages of seq_file private data

[stsp <stsp2@yandex.ru>]

08.11.2024 18:32, Kees Cook пишет:
> On November 8, 2024 2:13:38 AM PST, Stas Sergeev <stsp2@yandex.ru> wrote:
>> seq_file private data carries the inode pointer here.
>> Replace
>> `struct inode *inode = m->private;`
>> with:
>> `struct inode *inode = file_inode(m->file);`
>> to avoid the reliance on private data.
> Conceptually this seems good, though I'd expect to see the removal of _setting_ m->private too in this patch.

Done and sent v3.

>> This is needed so that `proc_single_show()` can be used by
>> custom fops that utilize seq_file private data for other things.
>> This is used in the next patch.
> Now that next patch is pretty wild. I think using proc is totally wrong for managing uid/gid. If that's going to happen at all,

And if not - it would be good if someone
tells how to fix the actual problem then.
I think the closest thing was credfd discussed
here:
https://lkml2.uits.iu.edu/hypermail/linux/kernel/1403.3/01528.html
But /proc/self/status already carries creds,
so what else is it if not credfd? :)
I can't even think of what else the read()
syscall should return on an actual hypothetical
credfd - other than what it returns now when
reading /proc/self/status.


>   I think it should be tied to pidfd which will already do the correct process lifetime management, etc.
Please let me know the exact scheme
you have in mind so that I can try it out.
I don't see any obvious mapping of my
current proposal to pidfd, so I can't guess.