Re: [PATCH bpf] bpf: Reject sleepable kprobe_multi programs at attach time

Kumar Kartikeya Dwivedi
2026-04-01T14:08:51Z

On Wed, 1 Apr 2026 at 15:49, Varun R Mallya <varunrmallya@gmail.com> wrote:
>
> kprobe.multi programs run in atomic/RCU context and cannot sleep.
> However, bpf_kprobe_multi_link_attach() did not validate whether the
> program being attached had the sleepable flag set, allowing sleepable
> helpers such as bpf_copy_from_user() to be invoked from a non-sleepable
> context.
>
> This causes a "sleeping function called from invalid context" splat:
>
> BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:169
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo
> preempt_count: 1, expected: 0
> RCU nest depth: 2, expected: 0
>
> Fix this by rejecting sleepable programs early in
> bpf_kprobe_multi_link_attach(), before any further processing.
>
> Fixes: 0dcac272540613d41c05e89679e4ddb978b612f1 ("bpf: Add multi kprobe link")

Please use the right format.
Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")

You can add the follow to your .gitconfig to generate the fixes tag.
[alias]
fixes = log -1 --format='Fixes: %h (\"%s\")'

> Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
> ---
> kernel/trace/bpf_trace.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 0b040a417442..af7079aa0f36 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2752,6 +2752,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> if (!is_kprobe_multi(prog))
> return -EINVAL;
>
> + /* kprobe_multi is not allowed to be sleepable. */
> + if (prog->sleepable)
> + return -EINVAL;
> +

Looks ok to me, Jiri, could you also take a look?

> /* Writing to context is not allowed for kprobes. */
> if (prog->aux->kprobe_write_ctx)
> return -EINVAL;
> --
> 2.53.0
>