Re: [PATCH bpf-next v2 0/2] bpf: Fix sleepable check for tracing prog

On Sat, Jul 25, 2026 at 6:27 AM Leon Hwang <[email protected]> wrote:
>
> When CONFIG_FUNCTION_ERROR_INJECTION is disabled, a sleepable tracing prog
> is allowed to attach to '__x64_'-alike prefix symbols.
>
> It is because the verifier does not verify whether the symbol is a kernel
> function or a bpf prog. That said, a sleepable tracing prog is allowed to
> attach to a bpf prog target whose name has '__x64_'-alike prefix.
>
> For example, a sleepable fentry prog attaches to a '__x64_sys_nop' XDP

we do have addr, so we should be able to distinguish between attaching
to kernel function vs BPF program, no?

> prog, and copies buffer from a user pointer with bpf_copy_from_user()
> helper. After attaching the XDP prog to lo interface, the kernel BUG
> could be triggered by 'ping -c 1 -W 1 127.0.0.1':
>
> [    3.460756] BUG: sleeping function called from invalid context at kernel/bpf/trampoline.c:1324
>
> Fix it by disallowing sleepable tracing prog always when its target is
> bpf prog.

what happens when we freplace sleepable BPF program/subprogram with
another sleepable BPF subprogram? And same question for sleepable
fentry/fexit program attaching to sleepable BPF program? Is it
something that just cannot work or we can actually allow that?

>
> Changes:
> v1 -> v2:
> * Drop redundant 'prog->sleepable' check.
> * Collect Acked-by from Viktor, Thanks.
> * v1: https://lore.kernel.org/bpf/[email protected]/
>
> Leon Hwang (2):
>   bpf: Fix sleepable check for tracing prog
>   selftests/bpf: Verify rejection of sleepable tracing prog
>
>  kernel/bpf/verifier.c                         |  9 ++-
>  .../selftests/bpf/prog_tests/fexit_bpf2bpf.c  | 57 +++++++++++++++++++
>  .../selftests/bpf/progs/fentry_sleepable.c    | 19 +++++++
>  tools/testing/selftests/bpf/progs/xdp_dummy.c |  6 ++
>  4 files changed, 88 insertions(+), 3 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/progs/fentry_sleepable.c
>
> --
> 2.55.0