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

Kumar Kartikeya Dwivedi
2026-04-01T14:43:21Z

On Wed, 1 Apr 2026 at 16:08, Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote:
>
> 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
> >

Also, please add a selftest.

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