Re: [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Apr 02, 2026 at 12:41:25AM +0530, Varun R Mallya 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: 0dcac2725406 ("bpf: Add multi kprobe link")
> Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>

nice catch!

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka


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