Re: [PATCH bpf-next v5 4/5] bpf: Make fs kfuncs available for SYSCALL and TRACING program types

[Alexei Starovoitov]

On Tue, Dec 10, 2024 at 6:43 AM Christian Brauner <brauner@xxxxxxxxxx> wrote:
>
> On Tue, Dec 10, 2024 at 02:03:53PM +0000, Juntong Deng wrote:
> > Currently fs kfuncs are only available for LSM program type, but fs
> > kfuncs are generic and useful for scenarios other than LSM.
> >
> > This patch makes fs kfuncs available for SYSCALL and TRACING
> > program types.
>
> I would like a detailed explanation from the maintainers what it means
> to make this available to SYSCALL program types, please.

Sigh.
This is obviously not safe from tracing progs.

>From BPF_PROG_TYPE_SYSCALL these kfuncs should be safe to use,
since those progs are not attached to anything.
Such progs can only be executed via sys_bpf syscall prog_run command.
They're sleepable, preemptable, faultable, in task ctx.

But I'm not sure what's the value of enabling these kfuncs for
BPF_PROG_TYPE_SYSCALL.